That was probably the good stuff... he was saving that for a special occasion. Kids' birthday, anniversary- etc...
Seriously though... what a fantastic natural camoflage. You're a snail eating bird in a lake- you look at that and you see an algae covered rock... not a snail.
I don't know anything about that kind of snail- or how common that is to be covered in algae- but it would be a fantastic defence mechanism in a population if they learnt to not eat algae off each other.
"DON'T eat my back I WON'T eat yours"
It's like how cadis fly larvae will build whatever sticks and stones the can find into their shells- and those crabs that decorate themselves in debris they find. Great natural disguise.
