Mr. Speidel decided to try female hormone treatment for Unk. The siamang would receive only a small amount of female hormones, not enough to produce female behavior or physical characteristics, just enough to reduce his aggressive behavior to the point where he would not attack Suzy when they met. Mr. Speidel knew that not only could hormones have an effect on an animal’s behavior, but also that a change in the animal’s social situation could have a permanent effect on hormone levels. In other words, hormones affect behavior, but behavior affects hormones as well. If, after hormone treatment, Unk formed a pair bond with Suzy, his normal siamang behavior in a normal gibbon arrangement might reduce his body’s overproduction of male hormones. For three days, Unk received daily treatments of female hormone. The following day he was given an injection of a stronger tranquilizer than he had received before. Suzy also received a small dose of tranquilizer in case memories of the two attacks made her nervous. Unk’s tranquilizer quickly took effect. The siamang slumped to the floor of his cage, half asleep. He was too groggy to protest as he was moved into Suzy’s enclosure. Suzy watched him warily, eyes wide, but made no effort to approach him. After a while, Unk began to stir. The effects of the tranquilizer were wearing off. Still sleepy and wobbly, Unk stood up. To the human observers, he looked as if he was about to attack once again. He must have looked that way to Suzy also, because all at once, she took matters into her own hands. Before the groggy Unk could reach her, she charged at him and bit him hard on the foot. Gentle Suzy had finally had enough. The zookeepers were amazed and pleased. And apparently Unk was, too. From that moment on, he made no attempt to attack. He accepted Suzy’s companionship and she accepted his. The introduction had been successful at last. The Milwaukee Zoo had a siamang pair. The question now became: Would this pair, raised by humans, understand enough about normal siamang behavior to breed and raise their young? By the time a week had gone by, it was hard for the zookeepers to remember why they had felt pessimistic about the siamangs. Unk and Suzy were truly a pair, and, typical of gibbon pairs, they seemed absolutely devoted to one another, head over heels in love. The siamangs played together, chasing each other all over their enclosure, and wrestling, squealing all the while. Watching them, zoo visitors sometimes thought that Unk and Suzy were fighting. In some ways, the siamangs’ play did resemble Unk’s terrible attacks on Suzy, but close observation revealed an important difference. Unk’s expression was not his aggressive face, but rather his play face. To make the play face, he drew back the corners of his lips in a kind of grin, but he did not open his mouth so wide as he did for the aggressive face. His imposing teeth did not show as much as they did when he threatened. During quiet times, Suzy and Unk often touched one another. They spent hours grooming together. They slept together on a shelf, hugging each other close. They embraced frequently, wrapping their long arms around one another. The siamangs loved the sun, and a favorite sitting place was a patch of cage floor where the sun’s rays entered through a roof skylight. When Suzy sat in the sunlight, Unk often sat down beside her and put his arm around her shoulders. Just like a wild pair of gibbons, Unk and Suzy had a territory to defend. Of course, their territory was man-made and there was no possibility of losing it to another siamang family. Neither of these facts seemed to matter at all to Suzy and Unk. They were as happy in their enclosure as any pair in the jungle, and every morning and evening they proclaimed their proud ownership of their home.