The rhinoceros constitutes a rare surviving example of megafauna, and grows in adulthood into an extraordinarly fast and powerful animal, dangerous enough when hunted to win a place in the African Big Five.
About a decade ago, I was living in Lincoln Park in Chicago, across the street from the zoo, which I was consequently able to frequent. One day, I was flabbergasted to see a zoo-keeper delivering a back-rub with a bristle push broom to a full-grown white rhinoceros, who was visibly ecstatic. One could see that this practice was a regular routine.
In fact, I found that the rhino would come trotting over expectantly, when out-of-doors in its sunken enclosure, if any human approached invitingly close to the fence. That friendly rhino was obviously hoping that someone else might volunteer to scratch her back.