If you quickly kill a mob that has 20 (❤× 10) health, the death sound will not play at all.

Steps to reproduce
1. Use a crossbow and shoot a mob that has 20 (❤× 10) health 2 times.
2. Punch the mob that has 20 (❤× 10) health and then shoot.

You only hear the 'hurt' sound if step 2 is done.