stammer
吃 centers on disrupted speech: stammering or stuttering, where words catch and repeat involuntarily.
吃 combines 口 (mouth) with 乞, which likely contributes the sound and may suggest a gasping or catching quality in speech.
The mouth 口 beside 乞, which looks like a person catching their breath, suggests speech that catches and stammers.
For キツ, imagine a stammering person trying to say 'kits' but getting stuck: kits -> キツ, and the mouth 口 keeps catching.