Shearer co-created, co-wrote and co-starred in Rob Reiner's film "This Is Spinal Tap" (1984). Shearer, Reiner, Michael McKean and Christopher Guest received a deal to write a first draft of a screenplay for a company called Marble Arch. They decided that the film could not be written and instead filmed a 20-minute demo of what they wanted to do. It was eventually greenlighted by Norman Lear and Jerry Perenchio at Embassy Pictures. The film satirizes the wild personal behavior and musical pretensions of hard rock and heavy metal bands, as well as the hagiographic tendencies of rockumentaries of the time. The three core members of the band Spinal Tap—David St. Hubbins, Derek Smalls and Nigel Tufnel—were portrayed by McKean, Shearer and Guest respectively. The three actors play their musical instruments and speak with mock English accents throughout the film. There was no script, although there was a written breakdown of most of the scenes, and many of the lines were ad-libbed. It was filmed in 25 days.