Well, if I'm writing in first-person past, then it's past tense, right? Right? This should be easy . . .

Here's the scoop: my POV character is telling a story that happened in the past, and part of that includes describing people's habits, skills, characteristics, etc. which is where the tense is tripping me up. For example:

He could do a pretty good cow impression when he got thoughtful.

I don't know whether to use the past tense (the slow chewing incident is occurring in the past) or present tense (the character is still alive by the end of the story and presumably hasn't changed up his mastication habits).

I suspect this is less of a grammar rules case and more of a storytelling craft issue, but I'm new to first POV and lost. Any words of wisdom?

You are magical people and I thank you in advance.