shut one's mouth
拑 centers on forcibly closing or clamping the mouth shut, often by hand or with a tool.
拑 combines 扌 (hand) with 甘, which likely contributes the sound and may relate to clamping or holding. The exact historical development is uncertain.
A hand 扌 clamps over a mouth 甘 (here representing an opening), forcibly shutting it.
For カン, imagine a can clamped shut by hand: can -> カン, and the hand keeps the mouth of the can closed.