I don't use letters

Simon is taking a bath. Uncle David, overseeing this activity, looks for the floating letters and other bath toys typically lying around.

Uncle David: Let's spell something. Where are your floating letters?
Simon: I don't use letters. Now I conduct scientific experiments.
Uncle David: Okay, let's do some experiments.

Simon proceeds to pour various amounts of water into a little plastic cup, examining the levels and then pouring out the water. When he covers the cup with a towel, the water doesn't spill when he turns it upside down. He was very pleased with the results of his experiments.