Enemies killed by the push-attack (the stab) of Kerillian’s Dual Daggers or Sienna’s Dagger never play death animations. I am referring to the actual stab itself, not the bleed component.
Just load into a mission, find an enemy, then kill them with the stab from either weapon’s push-attack. A death animation will never play, whether you kill with a headshot or a bodyshot. They simply fall down, limp.
I initially thought it was because of the bleed, but I tested other attacks that cause bleed and the animations still work. This may or may not be a bug, but regardless it’s an inconsistency worth fixing.