It's basicly a straight stick of some sort with a bend about 4-6 inches from the "business end". Typically, the stick is about a meter long, and the bend is usually somewhere around 45 degrees. I've heard rumors that a 90 degree bend is illegal here in MA, but I've never seen any hard evidence to that effect.
In any case, the idea is that you slip the stick into a lobster's hiding hole, and then tap the bug on the abdomen/tail with the bend it the stick, which makes it think there's something behind it. Most sensible lobsters, being helpless from the rear, will try to turn and face the hidden aggressor, which hopefully will require them to exit their hole and allow you to grab them. The tickle stick is not intended to be a mechanical lobster-prying tool so much as a lobster-fooling device, so I'm not sure what advantage rigidity would impart. When I use one at all, it's as often a bent coat hanger as anything else.