I've noticed something curious about the rotation of a rectangular prism. If I take a box with height $\neq$ width $\neq$ depth and flip it into the air around different axes of rotation, some motions seem more stable than others. The 3 axes which best illustrate what I mean are:

(1) Through the centre of mass, parallel to the longest box edge.

(2) Through the centre of mass, parallel to the shortest box edge.

(3) Through the centre of mass, parallel to the remaining box edge.

It's "easy" to get the box to rotate cleanly around (1) and (2), but flipping the box around (3) usually results in extra twisting besides the rotation around (3) that I'm trying to achieve (obviously a "perfect" flip on my part would avoid this twisting, which is why I call it an instability). If you're not quite sure what I'm talking about, grab a box or book with 3 different side lengths and try it out (but careful not to break anything!).

What's special about axis (3)?

![enter image description here](https://i.stack.imgur.com/yzD8c.png)
Image taken from [Marsden and Ratiu](http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.111.1838).