Follow Pearl, Malti & Bruce
There is no doubt that “the shell” is a very good design.
It is lightweight, attractive, sleek and stealthy.
Tired? Take a snooze inside your shell.
Looking for lunch? Hunker down in your shell to scope for snacks.
Looking like lunch? Snap shut and send the predator packing for greener (well, browner) pastures.
Depending on the threat level, one shell is often sufficient.
But there may be some threats where one shell is simply not enough.
In these cases, two shells is better.
Pearl, Malti, Bruce & their mama