The vast majority of 'irregular' stress renderings in Bridges' original dictionary manuscript seem to arise from just these five sources. It may be that these effects help to preserve morpheme boundary and identity information. For instance, given the importance of derivation of verbs from nouns and adjectives using -Vna- and -ata-, shifted stress allows one to differentiate these morphemes from lexical -ata- (common enough) and those -na-'s that are part of lexical roots (also relatively common). -Vna itself will often lose stress and reduce to a tense vowel before other suffixes, leaving the shifting as a hint of its underlying presence. Stress can also differentiate otherwise identical voice morpheme strings: tú:mu:- causative reflexive (get someone else to do/make one) from tu:mú:-(1) the causative of making oneself seem, or pretend to be in some state, and tu:mú:-(2) the circumstantial (tu:- allomorph before m-) of same (i.e. to seem/pretend at any specified time or place, with any particular tools, for any reasons, etc.). Circumstantial T has different allomorphs- some having following stressable vowel, others not- this also complicates matters for the learner but may also help disentangle morpheme boundaries for the listener. Sound symbolism There appears to be a great deal of remnant sound symbolism in the Yahgan lexicon. For example, many roots ending in -m encode as part of their senses the notion of a texturally softened positive curve (similar to -mp in such words as lump or hump in English), while an -l in similar position often shows up when the reference is to bloody core parts, often out from once safe confinement inside the body. Many roots with initial ch- refer to repeated, spiny extrusions, final -x to dry, hard-edged, or brittle parts, and so on. The historical sources of these patterns cannot be known for sure, but it may be possible that there was at one time a shape and texture classifier system of some sort behind them. Such systems are rather common in South American languages. There is little direct onomatopoeia recorded by Bridges, despite descriptions of highly animated imitative behavior on the part of speakers being recorded in the late 19th century. Several bird names are perhaps reduplications of calls (or other nonvocal behavior), and there are a couple of imitative cries and sound words. Most words denoting sounds end in an unproductive verb-deriving suffix -sha (in at least one case -ra, and r is known