When the teddy bear's music box runs down, Baby Eggs hands the mechanism to Fish who gives the key only two half-turns. The music box then plays again, with its key somehow able to unwind for many revolutions. Later on after the Boxtrolls wake up, this impossibility is repeated, but is even worse since now the key winds/unwinds in the opposite direction.
[on seeing Eggs scratching his crotch]
Winnie: NO! Don't scratch those in public! That's why they're called privates!