Hermit crab are often have spiral abdomen that is so vulnerable. What they do to protect their abdomen is by finding a shelter which is the shell of the sea snail. Such a stealer, lol! Obviously, their favorite hobby is climbing and it is very appreciative to see them in panic when you free them just like in the video.
As the hermit crab grows, it leaves the shell it permanently owned to search for new one! Also, they go to the water to procreate - living the egg in the sea to hatch.
Whew, whatta summer! Don't hurt it when you see, they are sociable creatures and tickly!