Here's why:
* Interjections are words or phrases that express sudden or strong emotion. They are often used to express surprise, disgust, joy, or other feelings.
* Shoo is used to tell something, usually an animal, to go away. It expresses a command or a desire for something to leave.
"Smack" is usually a noun or a verb, not an interjection. It can be used to refer to a loud sound, a hit, or a taste.