Back in the day when I owned guinea pigs, I witnessed this phenomenon:
- Guinea Pig 1 would run around the confines of the cage and whack Guinea Pig 2 in the butt, coming to a halt
- Guinea Pig 2 would then take off, repeating Guinea Pig 1's actions, and hit it in the butt, coming to a halt
They'd play it in the early morning often, usually at about 6AM.
After that they were seemingly normal abyssinian guinea pigs.