In the Valentine's Day 2011 event, one mouse would randomly turn into Cupid and had to shoot arrows at three mice to make them pink. These three pink mice would exchange gifts with the other pink mice and receive gifts from the others. Mice unlocked titles by exchanging gifts.
Every map, one mouse is randomly chosen to be cupid. Being cupid means you cannot get the cheese. ↑ to fly around, ↓ to shoot arrows. The goal is to shoot 3 mice at least, and turn them into "loved ones." Shooting has some knockback, too. "Loved ones" may receive gifts. Staying near other mice/hole is a good strategy to get gifts from other mice.
Cupid caused a bit of mayhem on maps, as mice would follow them around instead of trying to get the cheese. Since cupids could not get cheese and thus not go in the hole, it was advised for shamans to ignore them.