Talked to a vet tech about my cat's 'weird' staring and now I get it

My tabby Moe sits on the back of the couch and stares at the blank wall for 20 minutes every evening. I joked about it with my neighbor who's a vet tech in Dayton, and she said it's not him being weird, it's him processing sound. Apparently cats hear higher frequencies than us, so he might be tracking mice in the walls or even the neighbor's TV through the drywall. She told me to watch his ears next time, and sure enough, they swivel tiny amounts while he stares. That conversation made me rethink all the little stuff I wrote off as 'cat being cat'. Now I'm wondering how many other odd behaviors have a real reason behind them. Anyone else have a vet or tech explain something that changed how you read your cat's daily habits?