Calebite

I was teaching Caleb to brush his teeth, and after the timer I bought lasted 3 days before it broke, I suggested that Caleb sing "Twinkle Twinkle Little Star" three times to make sure he brushed for an appropriate amount of time.

"Okay.  I will sing that.  But I will have to sing in "fish."
"I'm sorry?"
"I will have to sing in "fish."  Because my mouth will be full of my toothbrush and toothpaste."
"What is "singing in fish?"
"It's when you say or sing in your head.  Because if a fish spoke, you wouldn't hear any sound because fish can't speak.  We count in fish all the time at school."
"Alright.  You sing in fish "Twinkle Twinkle Little Star" three times and then you're done."

Because I was there, I brushed his teeth myself, and sang in "fish" in my head to make sure three times was enough.  Halfway through the second time, Caleb put his hand on mine.

"That's three times."
"Oh, you must sing faster than I do.  You have to sing it at this speed."  I sang at a moderate tempo.
"I sang it faster, because I had to sing at the same speed that you were brushing."