Number Three?

In a public restroom tonight after explaining the expressions "number one" and "number two". . .

Me: "So do you need to make number one or number two?"

Anna: "Wait. What's number one?"

Me: "Wee wee".

Anna: "And what's number two?"

Me: "Poo poo."

Anna: {Long pause} "What number is diarrhea?"

And then i had to try to contain my laughter because it upsets her.You just can't buy that kind of entertainment!