I’ve used AI and copy/pasted the answer:
“Don’t look a gift horse in the mouth” is an idiom that means don’t be ungrateful or overly critical of a gift received, regardless of its value or the intentions behind it12345. The idiom refers to evaluating a horse’s age by looking at its teeth, which is rude to do when someone gives you a horse as a gift24. The polite thing to do is say “thank you” and accept the gift graciously145.