In south Italy is very common to eat them, they are a delicacy (and protected since you can't harvest them, except in particular places). When I saw them doing this stuff as a kid I was absolutely terrified, for some reason I never thought about them being alive.
Nature: "Hmmm, this little ball of life is kinda defenceless. Let's add a spike or two.
*a few moments later*
Am I the only one worrying about it suffocating?
A) I did not know they did this. B) ive always believed they were venomous so I've always been terrified of the little buggers and therefore have had mild panics when I see them in the sea.
Huh. I guess that’s what those little guys in Super Mario Bros. are.