Tommy, Beauty, and Baby had set up a harmonious household when a pet store offered an irresistible bargain in the form of an additional pair of young marmosets that nobody seemed to want because they had been injured at some time, the female losing a couple of inches of tail and the male two or three fingers from one hand. This led to a lesson in the social customs of marmosets. Beauty had not in the least minded sharing her home with Baby, but with the appearance of the newcomers there was trouble.

It began with Tommy, who apparently considered that a female with a bobbed tail was exactly what he wanted. He began making monkey-fashion passes at her, with struttings and touched noses. Beauty took cognizance of this intention of infidelity by attacking the newcomer so furiously that we had to get her out of there to save her life. That gave us two cages of marmosets, because we could hardly put the new female — who was tagged Sister — into another home without bringing her partner along. Tommy continued to gaze longingly across the room at Sister, plastering himself against the bars of his cage and going into a strut every time he could attract her attention until the infuriated Beauty would leap on his back and bite him. The question was not really solved until they had twins.