Giddyup!

This conversation occurred as we exited the freeway today.

Lucas: What's that big building?
Me: That's the place where people sit to watch the horses on the racetrack.
[He gave me a puzzled look, so I elaborated.]
Me: There's a track shaped like an oval and horses race around and around the track.
Lucas: Oh, I've been to a racetrack before.
Me: You have? [completely surprised] When?
Lucas: A long time ago. I was on one of the horses.
Me: You were?
Lucas: Yeah, don't you remember? And the horses went around and around.

Then I realized what he was talking about.