Mooch, hypercorrecting

[Mutts, March 7, 2019. Click for a larger view.]

Sorry, Mooch: who is correct. (Who told you that?) Whom for who, like between you and I, is a hypercorrection. Garner’s Modern English Usage explains:

Sometimes people [or cats] strive to abide by the strictest etiquette, but in the process behave inappropriately. The very motivations that result in this irony can play havoc with the language: a person [or cat] will strive for a correct linguistic form but instead fall into error. Linguists call this phenomenon “hypercorrection” — a common shortcoming.

Mooch’s gotcha “Ha!” and smug look in the third panel tell me that Patrick McDonnell, the strip’s creator, understands the difference between who and whom.