[paul.fr]

Mice are a few inches high, so how do they "shrink" their body to get underneath the small gap at the bottom of your door?

[another_someone]

Flesh is very maleable.

A friend of mine who used to do potholing suggested that any gap you can get your head under, you can find a way of manipulating the rest of your body through (the head has a rigid bone casing, and very difficult to compress; but the rest of you can easily be squeezed and manipulated to quite a substantial extent).

[Carol-A]

Yup... any mother will tell you, once the head is out the rest is easy!