The disparity in the dynamics of M1 and M2 can also be rationalized by invoking the dipolar nature of the lattice vibrations. Due to the polar character of the lattice, asymmetric phonon modes may be perceived as oscillating dipoles and, accordingly, phonon-phonon interactions as dipolar. Based on the assignment of M1 and M2 presented in Ref. 18, we recall that M1 primarily involves the motion of the iodide ions while M2 has substantial additional contribution from the motion of the lead ion around its equilibrium position. This indicates that the M2 mode, with its larger asymmetry, can induce larger lattice dipoles, and accordingly acquires greater anharmonicity. More detailed modelling of the lattice motion combining first-principles calculations and molecular dynamics, albeit being computationally expensive, can offer pertinent insights in this context.