First ‘Monsters University’ teaser trailer features Billy Crystal ad-lib

Showcasing one of many Billy Crystal ad-libbed lines, Yahoo! Movies has this exclusive teaser trailer for Disney/Pixar's "Monsters University."

This being the prequel to "Monsters Inc.," the story details how Mike (Crystal) and Sulley (John Goodman) first met in college. In what is essentially Pixar's family-friendly take on "Animal House," Mike and Sulley clash when they first meet as students at the University of Fear. The movie will show how the two got over their differences and formed their lifelong friendship.

While they were recording dialogue, Crystal improvised four lines -- all of which Pixar liked. Dan Scanlon, the director of "Monsters University," said, "[Crystal] gave us so much fun material, we decided to cut four slightly different versions of the trailer." In this cut of the teaser, as Mike sleeps he mutters, "My homework ate my dog." You can see all four edits on the "Monsters University" Facebook page and vote for which line you think is the funniest.

Steve Buscemi reprises his role as Randall in "Monsters U," as does John Ratzenberger (the Abominable Snowman). Newcomers to "U" include Ken Jeong ("The Hangover"), Kelsey Grammer -- who, by the way, is a "Cheers" alum like Ratzenberger -- and "SNL" alum Julia Sweeney.

Opening just over a year from now, "Monsters University" will be in theaters on June 21, 2013.

[Video: Watch the trailer for the original 'Monsters Inc.']