Ours love that too!
Once one gets on and you start spinnin it, the other will appear from nowhere and try and jump on while the chair is going full-tilt.
Dave tries to attack your hands while you spin the chair whch makes it fun for everyone!
(
Baj does Minecraft - http://www.youtube.com/w92baj,
Wed 15 Oct 2003, 19:52,
archived)