six apples but seven cats...

Teacher: "If I gave you 2 cats and another 2 cats and another 2, how many would you have?"
Johnny: "Seven."
Teacher: "No, listen carefully... If I gave you two cats, and another two cats and another two, how many would you have?"
Johnny: "Seven."
Teacher: "Let me put it to you differently. If I gave you two apples, and another two apples and another two, how many would you have?"
Johnny: "Six."
Teacher: "Good. Now if I gave you two cats, and another two cats and another two, how many would you have?"
Johnny: "Seven!"
Teacher: "Johnny, where in the heck do you get seven from?!"
Johnny: "Because I've already got a freaking cat!"