Level One: This would be the Three Stooges take.
Guy walks down the street, slips on a banana peel, falls down goes boom.
Maybe we laugh, but only out of dull habit. This rudimentary level of comedy, literally nuk-nuk and in-your-face in the Stooges' oeuvre, defies analysis because it's hard to be smart about stupid. Obviously, slapstick must have an element of cruelty. But cruelty + predictability is only mildly funny at best, although always reassuring.
Level Two: Compare how Chaplin would handle the same shtick.
Guy walks down the street, spots the banana peel, delicately steps over it, only to fall into an open manhole.
Well, that's a whole other brand of slapstick, a quantum leap, which invites analysis because the sight gag now works on so many different (and touchingly human) fronts at once. The joke has a dark subtext. You may avoid the obvious dangers, but another is right around the corner: Don't get complacent, life is a hazardous business. Here, cruelty + unpredictability is very funny, and never reassuring.
Level Three: What Mel Brooks Would Add to the Chaplin Version.
At the bottom of the manhole, cut to the crumpled tramp who, in the steep plunge, has broken his leg. He's not us – we laugh. Then, at the top of the manhole, cut to a well-dressed voyeur who, rushing to gawk, has broken his fingernail. He could be us – we don't laugh.
The actual Mel Brooks quote is this: "Tragedy is when I get a hangnail. Comedy is when someone else falls into an open sewer and dies." But you can see where he's leading us. At this level, slapstick has morphed into biting black humour, and it would take a supremely gifted director to pack an essentially verbal joke into a purely visual gag. Hard, but not impossible.
So that lone banana peel, in the hands of three different comic icons, comes with three very different punchlines. Stooges version: Slightly funny, and entirely comforting. Chaplin version: Very funny, and slightly discomforting. Brooks version: Witty, and thoroughly discomforting. As for, say, the Farrelly brothers, they'd have the guy slip on the banana peel, stumble but not fall, then pick up the yellow thing and stuff it somewhere – down his pants, probably. Comedy's not much on theory, but it's always in evolution.