At first, the Scrat was just a device to demonstrate how the actual ice age began. As the movie starts, his single-minded need to bury his nut creates a deep crack in the ice, causing a glacier to lurch forward. The Scrat shows up periodically afterward, victim of such natural disasters as a lightning strike and an avalanche.

[Chris Wedge] gives credit to character designer Peter de Seve, a New Yorker magazine cover artist, for originally inventing the Scrat. "Peter lives in Brooklyn and took research trips to the Museum of Natural History. Pretty early on, he came up with this little crazy guy, sort of a squirrel based on some lemur."

From sketch to Scrat: New Yorker artist Peter de Seve's drawing, left, was the basis of the animated version. The character is a cross between a squirrel and a rat.