When seeing a child run into the bathroom, close the door, and not emerge long past the time it takes for any sort of body function, go in IMMEDIATELY to investigate.
You see, I replaced the empty roll of toilet paper (see previous post) and Cal Henry thought he would see how much of the new roll he could unroll and fit in the toilet at one time. (Answer - a lot.)
So apparently there is a corollary to the aforementioned basic math -
NO flushing + silence from boys = TROUBLE.