What are YOs and what makes them go? They're cool, round things that love to spin fast and love to spin slow. "How do they stay on track?" kids ask as they play. It's 'magic' of course! (That's what you should say.) Just place one or both Twirly-YOs on the YO-Rail track piece. Then take the YOs for a ride.make 'em slide.go upside down.and 'round & 'round & 'round! It's a whole new spin on defying gravity! There's a crazy dancer character on one side of each YO and a cool visual effect on the other side. The YO-Rail track piece easily attaches to sections of the Spinnyos Giant YO-ller Coaster set for more spin-tacular fun! (Coaster sold separately.) How do YOs stay on the YO-Rail track? Well, it seems like magic, but actually there's a kid-safe magnetic axle inside the YOs that attaches to the metallic edge on the track. They're so much fun that once kids start spinning 'em, they won't want to stop! (You won't either - try 'em and see for yourself!) They're YO-tally awesome!