choke, smother
噎 centers on the physical sensation of something blocking the throat: choking, or being smothered and unable to breathe freely.
噎 combines 口 (mouth) with 壹, which likely contributes the sound and may relate to the idea of blockage or fullness. The exact historical development is uncertain.
The mouth 口 is blocked by the dense shape 壹, like a lump of food stuck in the throat. Picture trying to breathe but the airway is smothered.
For イツ, imagine the sound of a sudden choke: a sharp 'itsu!' gasp as air is cut off. The choked cry 'itsu' cues イツ while the mouth struggles against the blockage.