The original picture came from a link posted by burger_eater to an article at cracked.com called "15 Images You Won't Believe Aren't Photoshopped". Love that digging matchine (#15).
Anyway, on to the coconut crab. (All quotes from the Wikipedia article)
"The front-most pair of legs has large claws used to open coconuts, and these claws (chelae) can lift objects up to 29 kg (64 lb) in weight. The next two pairs, as with other hermit crabs, are large, powerful walking legs which allow coconut crabs to climb vertically up trees (often coconut palms) up to 6 m high."
So it could jump on you from above. And pick up many dogs.
"they will eat nearly anything organic, including leaves, rotten fruit, tortoise eggs, dead animals, and the shells of other animals, which are believed to provide calcium. They may also eat live animals that are too slow to escape."
Too slow to escape. Uh oh.
"Coconut crabs cut holes into coconuts with their strong claws and eat the contents; this behavior is unique in the animal kingdom."
I note that coconuts and human heads are about the same size, no?
Who else here is now thinking of the story "Sandkings" by George R.R. Martin? Better be nice to the coconut crab.
And, another picture (from Wikimedia. By the way, that thing it's climbing? That's a *coconut tree*"! AAAAAA! Enjoy the nightmares.