- Dominance: Guinea pigs are social animals and they establish a hierarchy within their groups. Climbing on top of another guinea pig is a way of showing dominance and asserting one's position in the hierarchy.
- Grooming: Guinea pigs spend a lot of time grooming each other as a form of social bonding. When one guinea pig climbs on top of another, it may be doing so to groom the other guinea pig's head or neck, which are areas that the guinea pig cannot easily reach on its own.
- Seeking warmth: Guinea pigs are small animals and they need to stay warm in order to survive. Climbing on top of another guinea pig can help them to stay warm by sharing body heat. This behavior is especially common during cold weather.
- Playfulness: Guinea pigs are curious and playful animals and they may climb on each other as a way to interact and have fun.