A group of snakes is generally called a bed, den, pit or nest, but a group of rattlesnakes is referred to as a rhumba or rumba. It's not entirely clear why it is called a rhumba, but the word comes from a Cuban Spanish term, rumba, which originally meant "party" or "carousel." Terms such as "bed" or "rhumba" are known as collective nouns when they refer to groups of animals.

More collective nouns for animal groups: