To knock or bump against something hard (often unintentionally)

To kowtow or touch one's forehead to the ground, especially in the phrase 磕头 kē​tóu.

(slang) To stand up to someone or go all out in a competition or confrontation.

To crack something between one's teeth, such as sunflower or melon seeds

To knock or tap something (such as a pipe or shoes) against a surface to shake out its contents

The sound of stones or hard objects hitting one another