thumping
Thumping is a dull sound produced when something impacts a surface that absorbs soundwaves. This sound effect is sometimes seen in vore to represent the muffled impacts of a struggling prey. It is also an alternative sound effect for a heartbeat.
Although this is an impact-related onomatopoeia (unless presented as "Thmp"), it is most likely better to use contact_onomatopoeia instead. Heartbeats probably should not be treated as impact sounds.
Sound effect forms: "Thump", "Thmp", "Tump", "Ba-thump", "Ba-dump", "Ba-dum"
If represented by "Thmp", or "Tump", tag as shortened_sound_effect.