^* According to space historian Asif Siddiqi, the Soviets preferred to train dogs for space travel, because apes were too excitable, too prone to catching colds, and “more difficult to dress.” And because Soviet space program bigwig Sergei Korolev loved dogs. Both the United States and the Soviet Union built a Tomb of the Unknown Soldier, but only Russia has a Tomb of the Unknown Dog (outside St. Petersburg), honoring the contributions of canine research subjects.