Grum are a species of which few members are left. The most notable Grum character is Dr Chef.

Grum are large and round, with balloon-like cheeks and long whiskers. They have six limbs, all of which are identical and can function as arms or legs. Rosemary compares Dr Chef to a cross between an otter and a gecko who walks like a caterpillar. Grum have branching windpipes, and six sets of vocal cords, and constantly vocalise a series of self-harmonising sounds that communicate their thoughts and feelings to others of their kind.

Grum change biological sex over the course of their lives. They start their lives as female, then transition to male, and end up somewhere in-between. The transition from female to male is a difficult time.

Grum were an old species, but a war among their kind has now reduced the population to the point that extinction is inevitable.