Why can't a NPC play animations while it has parts welded to it?

More specifically, it can't play animations while holding a weapon in it's hand. All other limbs play the animation, but any body part with a part welded to it is frozen... I've tried using a Humanoid to load the animation and an AnimationController, both with the same result.

Welds force Parts to stay in a single orientation, relative to a base Part. Animations do not override Welds. In order for an Animation to take precedence over a Weld, you need to break the Weld.