The Galley-oh-hoop-hoop is the mating ritual of a species indigenous to the planet Koozebane. The creatures' activities have been reported on twice, first on the 1974 special The Muppets Valentine Show, and again on The Muppet Show episode 107, but their species' designation has yet to be revealed.
The ritual itself involves the male and female charging toward each other, each howling their cry of supposed passion. Upon impact, the male and female instantaneously dematerialize, leaving a litter of four babies in their place. The Valentine version of the sketch featured a addional overture, where the male creature stood on it's head.
The spelling "Galley-oh-hoop-hoop" comes from The Muppet Show Book, which adapted the sketch in storybook form.