Karenin was not happy about moving to Zurich. “Dog time,” the narrator says, does not occur on a straight path but moves in a circular fashion, “like the hands of a clock.” Still, Karenin tried to establish his routine in Zurich, and he was “the timepiece” of Tomas and Tereza’s lives.
Karenin experiences time in a circular way, like a clock, thus he is happy. As Karenin brings this happiness and circular existence to Tomas and Tereza, he is their timepiece and the sole source of their happiness. Here, Kundera indicates that in some ways, human happiness is largely impossible, since human life is linear rather than cyclical.
One day, the phone rang and Tereza answered it. It was a woman asking for Tomas, and Tereza immediately began thinking of his infidelities. She knew the woman could have been a patient or a nurse, but this mattered little to Tereza. She began to believe that their relationship had been a mistake from the start. Anna Karenina had given him the wrong idea about Tereza, and they were, in fact, incompatible. Tomas was strong, Tereza realized, and she was weak. Tereza looked at Karenin and told the dog she was sorry, but they would have to move again.
While it assumed that the woman on the phone is one of Tomas’s mistresses, this is never confirmed. Still, the idea alone is enough to send Tereza back to Prague. She doesn’t believe that Tomas loves her in the way he says, and Tereza later admits that she leaves as a way to test Tomas’s love for her. If he follows her, then he loves her; but if he doesn’t follow, his love is not true and she is justified in leaving him.