  We present a study of the soft transverse optic phonon mode in SnTe in
comparison to the corresponding mode in PbTe using inelastic neutron scattering
and ab-initio lattice dynamical calculations. In contrast to previous reports
our calculations predict that the soft mode in SnTe features a strongly
asymmetric spectral weight distribution qualitatively similar to that found in
PbTe. Experimentally, we find that the overall width in energy of the phonon
peaks is comparable in our neutron scattering spectra for SnTe and PbTe. We
observe the well-known double-peak-like signature of the TO mode in PbTe even
down to $T$ = 5 K questioning its proposed origin purely based on phonon-phonon
scattering. The proximity to the incipient ferroelectric transition in PbTe
likely plays an important role not included in current models.
