An interjection can be followed by an exclamation point, question mark, period, or comma. It all depends on whether it stands on its own or if it's part of a sentence—and how dramatic you want to sound.
List of Examples
- whoa
- ew
- oops
- huh
- yikes
- wow
- hooray
- oh
- yum
- oy
Yeah, they look kind of sad without exclamation points. But, hey, maybe they are sad. You don't know their lives.