Actually, there's a little more to it than that. Ernie has a bowl of fruit and is counting each type of fruit in the bowl. Bert is next to him sorting his paperclip collection, and is getting annoyed at Ernie's counting, because he can't concentrate. Bert says he'll wait until Ernie finishes counting all the fruit, which Ernie does until his bowl is empty. Bert thinks he's done, but Ernie says he isn't finished. Bert asks him what else there is to count and Ernie replies "Watermelons". Bert remarks there are no Watermelons in the bowl, and Ernie replies, "That's right Bert. There are zero watermelons." Ernie then names off other fruit not in the bowl, each time noting there are zero of that fruit. Bert of course is frustrated, and walks off.