嗑

Left mouth radical 口 - anchors 嗑 in oral action. The defining act is using the teeth to crack something open: sunflower seeds, melon seeds, pumpkin seeds. The mouth radical correctly tags this as a teeth-and-mouth verb, in the same family as 啃 (gnaw), 咬 (bite), 嚼 (chew).

Right phonetic 盍 - supplies the sound (hé drifted to kè). 盍 itself is a literary fusion of 何不 (why not) and pictures a lid above a vessel. In 嗑 it serves only phonetically. The lid-and-vessel image has a tenuous mnemonic value - the tooth pressing down like a lid to crack the shell - but the connection is purely associative.