I want jelly bones too

I saw “Singin’ in the Rain” when I was a kid, but I don’t remember much of it apart from its classic main musical number, performed by Gene Kelly. After stumbling upon the next clip this morning, I’ve decided to watch the whole movie again. I was laughing out loud by the middle of the clip, and also feeling a terrible urge to start jumping around like a madman.

Didn’t try it, though: I’m not even sure some of those moves (and faces) are humanly possible. They should be, because they look natural and CGI wasn’t around in 1951 (right?). Which leaves me wondering: was Donald O’Connor human? Did he have jelly bones? Perhaps he was a Looney Tunes character in (a not very good) disguise? Judge for yourself:

And please, tell me your opinion… I’m really worried about this issue.