What makes the difference between live weight and dead weight?

For example, if a guy tries to pick me up and I’m struggling (kicking, squirming, etc), he can do it easily. But if I go limp, he almost drops me. Another example is picking up a cat (or other animal). Even if the cat doesn’t want to be picked up, it’s often still easier to do than to pick up a solid, inanimate object of the same weight. Can anyone explain this?