Wilhelmina, or "Hel", as Mongley mère and père prefer to call her, is a pet the Mongley family acquired after their move to Teras Terrace. Not all the monstrosities Pretorius Technologies accidentally brings to Earth or mutates people and other life forms into are of human-level intelligence and awareness; some of them are of more bestial mentality. These, too, the company tries to provide for, or at least get out of the way; some of them it puts into a zoo it maintains for the purpose at the edge of the Terrace, but the smaller and more innocuous (though "more innocuous" is a very relative matter) it may adopt out as pets to the Terrace's residents. Wilhemina is just such a creature, perhaps as intelligent as the average dog.
Due to the gyrous arrangement of her legs, Wilhelmina tends to spin in circles, but has enough variation in her speed in different directions to gradually move as she whirls around. Matters are little aided by the fact that her head is fully retractable inside her body and that she likes to run around with her head withdrawn, leaving her no way to see where she's going and causing her to careen around like an out-of-control bumper car. Her behavior that least endears her to the Mongley parents, however, is her frequent tendency to emit loud, disturbingly human-like screams at the least provocation, or apparently with no provocation at all.