What does a tree make that you'd want to put in your mouth? An apricot! Apricots are also about the size of an open mouth, so they kind of look like mouths hanging down under the trees. You can bite them right off the tree with your own mouth!
あん, きょう, こう
After you put the apricot in your mouth you realize that this tastes really familiar, but not pleasant. It tastes just like the anchovies (あん) from the zoo (ず) smell. How did that happen? You don't like apricots anymore.