The problem with animation writers, one of the many problems, is that they don't write visually. For them visual writing means lots of chases or excuses for fast cuts. When I think of visual writing I think of schtick.
Schtick has a lot to do with funny acting and funny situations. It's about small things, like the inability to find the sleeve of the jacket you're putting on. Or maybe your guy drops his wedding ring into the soup of the bully sitting beside him and has to fish it out with his fingers without the bully noticing. Small stuff like that.
Schtick is great, and animation is tailor-made for it, but it takes some skill to integrate it into a larger plot and most writers don't want to be bothered.
In the sketches above (which are hard to interpret...forgive me, I'm too sleepy to redraw them for clarity) I tried to imagine what kind of schtick a man without control over his arms and hands would do. Imagine putting your arms behind your back and letting a friend substitute with his arms. If he was well-intentioned he could try to make his gestures fit what you're saying but it would be off somehow...somehow out of sync and wrong...but funny in a strange way. Now imagine what your own arms would be like if they were naturally independent like that, without the aid of a friend.
Imagine what it'd be like if your arms had a mind of their own. While you're talking to friends the hand might become bored and squeeze your face, or they might squeeze the girl next to you. There's no telling what mischief they could get into.
Or maybe it's played more subtle than that. Maybe you underplay it so the audience senses something's out of whack but they can't put their finger on it. Anyway, you see what I mean. Schtick is fun.