Marcia, Cindy and Carol are not happy about Greg bringing one home for his science project. Jan, on the other hand, finds him super cute...as well as a good way to scare her sisters. Marcia and Cindy change their minds by the end of the episode, though.
Alice, on the other hand, is extremely afraid of mice and calls the exterminator when she sees the mouse, unknowing whether it is Greg's science project or if the house is overrun by mice.
Everybody Laughs Ending: Except for Robert Reed, who wrote a lengthy critique about why he thought said scene Alice outsmarting herself over the ink stain on the uniform was inane bullshit. Said critique was published in Barry Williams autobiography I Was a Teenaged Greg.
Humiliation Conga: Alice, when she realizes the supposed gag ink stain is a real ink stain.
Idiot Ball: Alice, who in the tag scene apparently cannot tell a gag ink stain from the real thing ... and one of her uniforms is ruined as a result; she thinks Jan was still full of practical joking fun and had placed the stain there ... only to find she had left an ink pen with the cap off inside the pocket.