Rosalyn is perhaps the only character in the strip whom Calvin really fears (other than Moe, the school bully). Introduced in an early strip, Watterson found her ferocity and intimidation of Calvin surprising, and he brought her back periodically in increasingly elaborate story-lines. Watterson described their relationship as "one-dimensional", although in her final appearance Rosalyn agrees to play a game of Calvinball, and in so doing, becoming the only character in the strip, other than Hobbes, to truly engage with Calvin on his own terms. Calvin is often terrified of her, calling her a "sadistic kid-hater" and a "barracuda in a high-school-senior suit"; but in the final Rosalyn story, their opposition is averted by a game of Calvinball, which Rosalyn wins. In nearly all the "Rosalyn stories", Rosalyn is shown demanding advance payment and raises in wage from Calvin's parents, supposedly to pay for college or for the hard work necessary to control Calvin. (For the same reason, she briefly appears as Calvin's swimming instructor.) In at least four stories, Rosalyn telephones her boyfriend, Charlie, to cancel prearranged meetings which she cannot fulfill. (Charlie remains an unseen character.) Calvin sometimes urges Charlie to stop courting Rosalyn, on grounds that Rosalyn is sadistic and/or insane. The collection Revenge of the Baby-Sat took its name from a storyline in which Calvin steals her study notes and threatens to flush them down the toilet bowl. Rosalyn's demands for higher pay to baby-sit Calvin have often been met with a small discussion between his parents. In one skit the mother tells her husband, "Pay whatever it takes to get us out of here for the night." In the last cell of the Revenge of the Baby-Sat storyline, after paying her and looking into his now empty wallet, the father says, "Are you sure there's nobody else in this town willing to babysit Calvin?" To which the mother says, "Maybe you would like to spend a week on the phone?" Other characters The cast of principal, recurring characters in Calvin and Hobbes is limited; for example, in the Yukon Ho! collection, only five regular characters appear. Other characters who make infrequent or one-off appearances include the following. Living food: Calvin often imagines that an oatmeal-like food comes to life, sometimes attacking him (or, in one case, reciting Hamlet's "To be, or not to be" soliloquy). Bill Watterson has said that his inspiration for this came