Speed, definitely kills.Some of what folks are attributing to hydrostatic shock is also covered in 'temporary wound channel.'
If you watch ballistic gel performance, you will see a large 'temporary' wound channel open up that then closes up after the bullet passes through. If that 'temporary wound channel' happens to be larger in diameter than the object you are shooting... then it's not temporary! Though skin is tough and can hold a lot in... even on a wood chuck.
Even back to Civil War days, the medical reports of .58 caliber Minie's completely cuttong off arms and legs is in part due to the temporary wound channel. And these were not high-velocity, high-performance bullets. But they did flatten and promote huge energy transfer, especially at closer ranges.
Somewhere I have a picture of a large woodchuck I shot earlier this summer with my .14 Eichelberger. 12 or 14 grain bullet (Can't remember which) at well over 4500 FPS and the woodchuck was cleved nearly in half. Range about 40 yards. The energy transfer and velocity opened up a wound channel that was much wider than said woodchuck. Pink mist indeed.
Terminal ballistics is a fascinating area... and as most folk shoot steel or paper, one that is mostly irrelevant. Where it is very relevant is in hunting (clean kill is an ethical hunters responsibility) as well as in .mil and .le worlds, especially in situations where the shot must leave no room for a target to respond. Typically, the only reliable way to do this is a medulla hit. So a lot of terminal ballistics has focused here in recent years. But also in the 'regular' military ammo, etc.
Huge resources was put into the subject in the 1960's and resulted in the adoption of the .223. Also the Soviets put a lot into terminal ballistics when they adopted the 5.45mm, which had an air pocket in the tip. Those were very feared in the 1980's Afghan war because of the horrific wounds they inflicted. IIRC, there was even some discussion of whether those rounds with air gaps and steel pins violated the Geneva Convention (or similar accords). Not sure what was decided. But I seem to remember there were protests about the use of the 5.45 in A-stan back then.
The short version is that there have been millions spent on studies... entire forests cut down to write reports. It's all publically available. And probably, folks are still learning things!
Interesting thread... not that it will 'solve' anything. But it's a fun rabbit hole.
Sirhr
Totally intuitive verbiage attributed to observation. Not everyone is a physimachist, but they are observers! 
