You want to get a scooter so you have one of yourself (oneself) and another self working together to choose. The two tiny yous sit on each of your shoulders and argue about which scooter you should choose.
Suddenly your selfs both gasp and choose the scooter in front of you that looks like a centaur (せん). The scooter is designed like a human on the top, the bars are its arms, and the bottom with the seat and the wheels are all horse. This centaur is what you choose to ride.