Fulminic acid (HCNO) has influenced the development of chemistry for over 200 years. Its explosive salts were first discovered in 1800 by Edward Howard, who appropriately called them "fulminating" after a Latin word meaning "to strike like lightning." The chemical composition of these salts piqued the interest of Liebig, who discovered in 1824 that silver fulminate was identical in composition to the silver cyanate compound prepared by Wöhler. As such, fulminic and cyanic acids became critical early examples of the emerging concept of chemical isomerism. The structure of fulminic acid was elusive for well over a century, 1,7-20 as many false starts pursued a two-carbon species, but in 1966 an IR spectral analysis of gaseous fulminic acid finally proved it to be a tetra-atomic molecule with H-C-N-O connectivity. Over the next four decades herculean efforts toward the accumulation and analysis of high-resolution rovibrational spectra revealed fascinating peculiarities in the quantum states of fulminic acid arising from large-amplitude H-C-N bending motion. The molecule was initially deemed quasilinear, a designation given to species with a nonlinear electronic minimum but a low barrier to linearity that gives rovibrational spectra characteristic of a linear framework. However, HCNO was later designated as quasibent, meaning that it possesses a linear electronic minimum but has an effective one-dimensional, double-well H-C-N bending curve that yields spectra bearing signatures of a bent structure. The mercurial quasilinear/quasibent nature of fulminic acid has thus become a testing ground for methods of modern chemical physics. Electronic wavefunction computations over the years have given muddled results for HCNO, as the geometry and vibrational frequencies exhibit an unusually strong dependence on both the orbital basis set and electron correlation method. In 1982, an MP3/6-31G** study found a linear equilibrium structure for HCNO; in contrast, MP2/6-31G** computations in 1989 gave a bent geometry with a barrier to linearity of 0.64 kcal mol -1 . A more comprehensive investigation in 1991 further revealed the difficulty of the problem. In particular, both the 6-31G** and 6-311G** basis sets produced linear structures with MP3 and CISD but bent geometries with MP2 and MP4. Moreover, MCSCF/DZP computations predicted a bent molecule, while MRCISD treatments built on these MCSCF wavefunctions spawned either linear or bent structures depending on the reference space employed. The gold-standard CCSD(T) method was applied to HCNO several times between 1992 and 2009, and the results varied dramatically with basis set. A TZ2P basis gave a linear structure in 1992, while the cc-pVQZ selection produced a bent molecule in 1996. More recent computations applied both frozencore and all-electron CCSD(T) with the cc-pVXZ (X = 2-6) and cc-pCVXZ (X = 2-5) series of basis sets. The optimized H-C-N bending angle varied nearly 30° over the series, but as the complete basis set (CBS) limit was approached, the molecule evolved to a linear structure. Our fresh 2024 investigation was the first to apply high-order coupled cluster theory beyond CCSD(T) to the fulminic acid problem. Wavefunction methods as extensive as CCSDT(Q), CCSDTQ(P), and even CCSDTQP(H) were employed in conjunction with the cc-pCVXZ (X = 4-6) basis sets and assorted CBS extrapolations to definitively ascertain the equilibrium structure, harmonic vibrational frequencies, and enthalpy of formation of HCNO via focal point analyses (FPA). Striking fluctuations of the ω5 H-C-N bending frequency were observed in the all-electron correlation series with CBS extrapolation: ω5(p) = (604, 260i, 334, 120, 146, 49i, 52, 45) cm -1 for [HF, AE-MP2, AE-CCSD, AE-CCSD(T), AE-CCSDT, AE-CCSDT(Q), AE-CCSDTQ, AE-CCSDTQ(P)]. The inclusion of scalar relativistic effects (MVD1) further decreased ω5 such that the final Born-Oppenheimer AE-CCSDTQ(P)/CBS + MVD1 ω5 frequency was merely 19 cm -1 . Although usually considered auxiliary effects, core electron correlation, the diagonal Born-Oppenheimer correction (DBOC), and MVD1 terms were all found to significantly influence whether vibrationless HCNO is linear or bent. Because our 2024 computations on HCNO were pushed to the ab initio limit, highly accurate benchmark data finally exists for this species. The vexing fulminic acid problem attracted attention 30 years ago from electronic structure method developers during the exuberant period in which density functional theory (DFT) first gained popularity in computational chemistry. In 1994, Handy, Murray, and Amos 76 wrote a paper entitled "Does Fulminic Acid Have a Bent Equilibrium Structure?" and attempted to answer this question by applying the SVWN and newly-minted BLYP functionals in conjunction with DZP, TZ2P, and TZ2Pf basis sets. With the best basis set (TZ2Pf), SVWN essentially gave a linear structure, while BLYP yielded a bent molecule with an H-C-N angle of 161.9° and a barrier to linearity of 16 cm -1 . An analysis of basis set trends suggested that BLYP retains a bent equilibrium structure in the CBS limit. Under the mistaken belief that the BLYP ω5 = 237 cm -1 prediction is close to the true harmonic frequency for the H-C-N bending mode, the authors concluded that the BLYP prediction of a bent structure was correct and that "modern DFT has a role to play even in the study of the most delicate properties of small molecules." What is most striking about the paper is its highly optimistic perspective about the capabilities of Kohn-Sham (KS)-DFT: "We recall that in principle the KS method includes all correlation effects (double, triple, quadruple replacements and beyond), and there is every hope that, as functionals are improved, they will all be truly represented." Even though KS-DFT has emerged as the most popular electronic structure method in computational chemistry, its viability for problematic molecules such as HCNO is still an open question. Therefore, in this paper we consider the following essential question: can the ladder of current DFT methods converge on a definitive set of predictions for fulminic acid, or was the optimism expressed by the Cambridge group three decades ago misplaced? Fulminic acid DFT results published after 1994 are surprisingly sparse. A 2022 study by Planells and Ferao 78 includes an optimized structure for HCNO at the B3LYP-D3/def2-TZVP level with a near-linear ∠(H-C-N) = 178.8°. In 2023, Bégué and coworkers provided HCNO optimized structures and harmonic vibrational frequencies for three methods: B3LYP/6-311G(d,p), B3LYP-D3BJ/6-311++G(d,p), and M06-2X/6-311G(d,p). In all three cases, HCNO is linear with ω5 H-C-N bending frequencies equal to 241, 268, and 398 cm -1 for the B3LYP, B3LYP-D3BJ, and M06-2X functionals, respectively. Fulminic acid is a member of the W4-11 benchmarking dataset developed by Karton, Daon, and Martin, which has been employed in numerous DFT studies. However, individual data for HCNO or other molecules are not typically reported in benchmarking papers. Moreover, equilibrium structures and vibrational frequencies are given far less attention than energetic properties in the DFT benchmarking literature. Recent developments in DFT have been extensively chronicled. In principle, DFT is exact, but the true exchange-correlation functional remains elusive, requiring reliance on density functional approximations (DFAs). The degree to which DFT is systematically improvable has been hotly debated in the literature, and disagreements abound as to whether there is indeed a hierarchical "Jacob's Ladder" leading to DFT heaven. Nonetheless, members in the zoo of existing DFAs are ubiquitously classified in terms of sequential rungs in a ladder. Large DFT benchmarking studies generally confirm the improved performance of higher-rung methods, but as analyzed by Gould and Dale, 86 large and diverse datasets can neglect instances where DFT approaches fail badly and can give a misleading sense of security. Given the historical prominence of fulminic acid in the history of chemistry and the lack of comprehensive DFT computations on this species thus far, we present here a detailed analysis of the performance of current DFT methods as applied to this notorious molecule. In particular, we analyze HCNO equilibrium geometries, corresponding vibrational frequencies, and HCN + O( 3 P) ® HCNO reaction energy to determine whether 473 DFT methods in current use provide any consensus or convergence on the quasibent/quasilinear nature of fulminic acid.