Jakub: "Daddy, you have a big tummy."
Pavel, jokingly: "No, I have a small tummy. Mommy has a big tummy." [Waits a beat, then]: "No, no, no, no. Mommy doesn't have a big tummy, she never has a big tummy. Never say that."
I have to say, he's getting quicker. This time, it only took him a couple of seconds to realize his folly. A few years ago, I would have had to point it out to him. At this rate, he may actually learn to think BEFORE he speaks by the time we're 90.