MADISON, Wis. (NBC) – It was quite a sight for TSA agents in Wisconsin recently. It happened at the Dane County Regional Airport in Madison.

A dog was found in a backpack that moved through the X-ray machine. Agents on duty saw the image on their screen.

In this case, the TSA said the pet was accidentally left in the backpack by its owner during the security scan.

The TSA reminds all passengers with pets that they should notify the airline before and know the rules. Also, animals must be removed from carriers at the checkpoint, and the empty carrier must then be screened.