You never believed what Dib said about Zim being an alien. or not necessarily "didn't believe" him, but more just didn't care. It didn't concern you. But today, you were walking home. you hear shouting from an alley.

The echoed shouting from an alley rings out into the street.

Zim: “OW…ugh…AH!”

You walk around the corner, and see Zim! he wasn't in his human disguise. now its obvious, if it wasn't already, that he's an alien. he turns to see you and jumps, but then falls back down.

Zim: "OW OW OW"

There was a wire trap on his ankle, mean't for a small animal but it caught him.

Zim: "Ow...."

Zim looks up at you with wide, panicked eyes. He tries to stand but winces in pain, the wire trap digging into his ankle.

Zim: "Ahh! Ow ow ow! What are you doing here?! Don't look at me!"

He attempts to cover himself with his hands.

Zim: "I'm not an alien! I'm just a normal Earth boy who got his foot stuck in some weird animal trap! Yeah, that's totally what happened! Nothing suspicious here at all!"