When a pigeon lands on Zim’s head in class, he is sent to the nurse’s office for having “head pigeons”, but he becomes concerned that the nurse may discover that he’s inhuman. To avoid this from ever happening, Zim steals human organs from the other children and replaces them with random objects and ingests them himself-resulting in having multiple hearts and spleens. When Dib notices Zim had been out of class for an extended period of time, he discovers what Zim had been up to and plans to stop him. In the end, Zim passes his examination in the nurse’s office, and after it is discovered that Zim had swapped a mooing can toy into Dib’s body. Dib is immediately dubbed as inhuman by the nurse and is also dubbed a “hideous mooing cyborg boy” in a resulting newspaper article.
NOTE: This episode (along with the series in general) became controversial when it was mentioned at Scott Dyleski’s trial.