
This is a hard haiku constraint because CLACK is pure sound, and sound-words can flatten a poem if everything before them exists only to justify the noise. The stronger entries solve that by giving the sound a clear physical source and a real consequence. auntie jj’s “FEIGN cool, TALON springs / bird of prey BRAWL, claws CLAMP / beaks CLACK together” is a strong example: the constraint words are absorbed into one coherent predatory action, so CLACK arrives as impact, not ornament. Across the set, the better poems make the target word serve as strike, taunt, verdict, collision, or contact, which is what keeps the haiku from becoming mere sound effect.