What are some of the parody in hitchhikers guide to the galaxy?

The singing dolphins are a parody of musicals in general. The musical cue enters from somewhere off-screen, and the dolphins begin to sing and dance. They swim in synchronized rhythm, and there are even brief interludes to allow for a child and a woman to have their respective solos. The musical number ends with a crescendo as the dolphins fly out of the water and into space.