Invader ZIM (2001)

Season 1: Episode 13

While at skool one day, Ms. Bitters tells the class that they need a new pet hamster due to the orders of the skool’s board of directors. When the hamster arrives, all the children love the hamster because of how adorable it is, in which Zim decides to exploit that fact since the hamster could help make the humans too weak to resist him. Zim plants an Irken device on the hamster that will permit it to grow larger and be controlled by Zim, but when the hamster grows rampant and breaks free, Zim must attempt to stop the huge hamster from destroying his headquarters, all the while worrying about the growing military presence that may have no choice but to attack the hamster, which would ruin all of his efforts.