Running out of Toots

One of Micah's favorite sayings is that he is running out of gas. Meaning he is too tired to keep walking, riding his bike, picking up toys, etc. In other words, it is his current favorite excuse. This morning we were driving to a friend's house and passed by a gas station. Micah was in one of his silly moods.
Micah: "Mom, do we put gas into the car's mouth?"
Me: "No, it goes into the gas tank."
Micah: "Wouldn't it be funny if we put gas in our mouths."
Me: (rolling my eyes) "Yep. That would be funny."
Micah: "Would it be funny if we put gas in our tummies."
Me: "Sometimes we do have gas in our tummies. Then it comes out our bottoms like toots."
Micah: ... thinking... "Sometimes I run out of toots."