system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If humans and dolphins are the only mammals that procreate for fun, why does my dog hump my leg?
gpt
Dolphins don't procreate for fun. The "dolphins and people do it for fun" saying comes from the fact that we are the two animals that procreate outside of ovulation period when the mating will not result in a baby. Other animals may find sex enjoyable or pleasurable but don't participate in sex outside of the female's ovulation period. This is partially due to the fact that sex increases vulnerability and uses a lot of energy.