In "Frosty the Snowman", which part of Frosty brought him to life?

"Frosty the Snowman” is a popular Christmas song written by Walter "Jack" Rollins and Steve Nelson, and first recorded by Gene Autry and the Cass County Boys in 1950 and later recorded by Jimmy Durante. It was written after the success of Autry's recording of "Rudolph the Red-Nosed Reindeer" the previous year; Rollins and Nelson shipped the new song to Autry, who recorded "Frosty" in search of another seasonal hit. Like "Rudolph", "Frosty" was subsequently adapted to other media including a popular television special.

The song recounts the fictional tale of Frosty, a snowman who is brought to life by a magical silk hat that a group of children find and place on his head. Frosty enjoys roaming throughout town with the children who constructed him, only stopping once at a crosswalk when the policeman directing traffic orders pedestrians to stop. Frosty finally says goodbye to the children and comforts them, promising he will be back again someday. Although Autry's original recording does not explain the reason for Frosty's departure, later versions have lyrics that attribute it to the hot sun.