Mutt wore his motorcycle cap together with his black leather jacket when he arrived at Bedford's train station on his motorcycle to look for professor Jones. When they came to Arnie's Diner, Mutt laid the cap on the table and placed the photograph of Harold Oxley and himself into it after having shown it to Jones.
When they were forced by the Russian KGB agents to leave the diner, Mutt took the cap with him. He gave it to Joe College, one of the students hanging around in the diner, saying "hold that", and then socking him in the jaw. In the fight arising therefrom, Mutt and Jones could escape, but the cap was lost.
Behind the scenes
The cap was manufactured by Baron Hats in Burbank, California. Different designs were taken into account, among others a cap worn by George Clooney in the 2008 movie Leatherheads. In the end, however, the decision was in favor of a classic motorcycle cap of the 1950's, with its "rattlesnake" expandable band, "pillowed" fabric crown, and black leather visor.
Mutt's cap is an eight-panel, soft-crown cap with a button at the top. It is made of Irish camel-hair textured wool and has a black leather visor and a chrome-plated hat band secured over the temples with American eagle buttons.
Marlon Brando had worn a similar cap when he portrayed the outlaw biker Johnny in the 1953 movie The Wild One. Since Mutt also wore a similar jacket as Marlon Brando, his arrival on his motorcycle at the train station quite resembled Brando's appearance in the movie.