Owen Long has contributed an interesting program that displays the odd
behavior of a book rotating in 3D space, now available in the Contributed
section of vpython.org.
Because there are no torques acting on the book, the (vector) angular
momentum does not change, but the (vector) angular velocity does change,
and the visual effect is that the book tumbles in an unexpected way.
You can see this effect in the real world. Try flipping a book or a tennis
racket in the air. You'll find that if the object rotates around its long
axis or the axis perpendicular to the largest side, the rotation is stable.
If however you flip it around the third axis, no matter how carefully you
try to flip it exactly around that axis, you'll see that the object tumbles.
P.S. Steve Spicklemire and I believe that we're very close to the next
release of the wxPython-based VPython 6. All that remains is some
documentation and some cleanups of keyboard issues.