why the corner pieces of bars of chocolate keep ending up in the middle when they are broken up with the wrapper on and then opened.

it's one of the big remaining mysteries of the universe.

much like the way underpants predominantly turn themselves inside out in the washing machine despite not starting off that way.

if you could provide a visual explanation? Nice drawing/photo or something?

not easily.

eaten that end of the chocolate bar now!

Well, that's the way to deal with a chocolate bar. Just eat the evidence...

had the least idea they did that.
Ah well, s'pose I'll have to get off my ***** and procure some!

it’s because the corners are the most constrained part of the wrapper and jiggling will gradually move pieces out of the corners.