Episode Title:Bad, Bad Rubber Piggy.Episode Description:By using a time portal device, Zim hopes to make a hunter-destroyer machine travel back in time and kill Dib when he is a small child so he can't interfere with his plans in the future. However, Zim discovers that he can't personally travel through time, but he can send objects through the portal, which end up exchanging places with objects in the past: when Zim throws a rubber piggy into the portal the first time, it replaces a tricycle Dib had been riding when he was a small child and in pursuit of an alien, which turned out to be a kiddie bop-bag; as a result, he crashes the piggy (which had replaced the trike) and becomes maimed by the accident. Zim continues to send a series of rubber piggies into the past to harm Dib until he is reduced to a catatonic state. However, this provokes Dib's father into building high-tech cyborg battle armor to protect his "accident-prone" son. Now the effect is reversed; when Zim sends a rubber piggy back, Dib gets even more badly hurt which makes his father redesign the armor to become even more resilient and dangerous. To stop this entire chain of events from happening, Zim sends a pig back to himself with the message not to use the portal device. Unfortunately, as the piggy must replace an object in the past, the piggy supplants Zim's brain. Zim is now reduced to the mental status of a three-year-old (which raises the question of how he could possibly send the piggy back to replace his brain; see the Grandfather Paradox).