The nice lady squatting in the “home products” aisle to comparison shop for mop heads looks up and smiles at Cooper, my five-year-old. He responds with, “What’re you looking at, Monkey Butt?”

The nice lady looks too young to have children of her own, probably too young to be comparison mop shopping. She’s not smiling now. I really hope that I look as shocked as she does. That way she won’t think that my young son is a serial thrower of simian epithets.

Monkey Butt? Where did that come from? I decide to get to the bottom of it. Hem.

My debriefing after the Episode was calm but firm. I was determined to find out how that particular phrase entered Coop’s vocabulary. Because, however, he is a third child, direct interrogation was fruitless. He has long known the cost of exposing your sources. When I asked where he heard those words, he just shrugged.

I continued my investigation by drawing up a list of likely suspects.

1. Baba — as my son’s grandmother is affectionately known, has been babysitting a lot lately. That nice old lady facade can fool some people, but I’m asking the tough questions. This file remains open.
2. The Media — I can easily imagine Hannah Montana saying something like that. So the TV is only going to show sports from now on. Also, everyone else blames them. Investigation ongoing.
3. His Mom — swears like a sailor but hates animals and is the reason that the children are not allowed to have a dog. So “Monkey Butt” would be an improbable way for her to go. A possibility, however.
4. The Siblings — would first have to acknowledge his existence, but clearly are in control of this kind of slang. “FAIL” is evidently a popular phrase with the young people these days. I hear that a lot. File open.

As the investigation deepened, a cloud of suspicion descended over the cousins, as it often does. First of all, it’s easy to blame them because they live really far away. Second of all, I have deep misgivings about my brother-in-law who recently gave up meat.

Finally, a breakthrough. Turns out, a little bird taught it to him. The parrot in Home Alone 3 (post Macaulay Culkin, actually) is to blame, repeating the phrase several times during the movie — a piece of media Cooper watched with his mother, his siblings, and his cousins. Only Baba comes away clean in this one. I consider the Case of the Mystery Monkey Butt closed.