Japanese monkeys have a close relationship with deer there, often riding them for transportation, while providing the deer grooming or food in exchange. But scientists have recently noticed something else: Female Japanese macaques are climbing onto the deer’s backs and grinding.
Researchers observed the adolescent monkeys mounting, thrusting, and making sounds that were typical during sexual interactions between monkeys. Most deer were nonchalant, continuing to eat or stand passively during the thrusting. In some cases when the deer walked away, the female monkey “displayed sexually motivated tantrums which consisted of crouching on the ground, body spasms and screaming, while gazing at the deer,” according to the researchers.
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https://qz.com/1160001/scientists-think-japanese-macaques-monkeys-are-practicing-sex-with-sika-deer/