Buster doesn't bark at every stranger. Just that one. Because he was scary.

When they get to the supermarket, Buster knows what he's supposed to do. When Autor picks his cart, Buster quickly gets into the bottom compartment to stay out of the way. He watches everybody walk past, yipping a few times when Autor passes something he should get.

This isn't the same supermarket they usually shop in though. It's a weird, new place, full of weird new smells, and lots of kids that want to stop to pet him.