Turn On the Lights (song) Puns

My dad points out the humming from the light over the table, since it's a fluorescent light. He turns to my sister and says "do you know why it's humming?"

Now, my father has been an electrical/mechanical engineer for going on 20 years. My sister is 7, so I expected him to tell her about voltages and whatnot.

But no, he says "Because it can't remember the words to the song."