This is a coconut in the process of sprouting. It's sent out a small shoot through one of the three 'eyes' at the top of the coconut shell, and soon it will send out some roots through another one.
The roots will go down, while the shoot stays up, so the shell will remain on the ground but keel over, as the roots take hold.
The bubble, buwa, is the conversion of the water and flesh inside the coconut shell into an embryo of the future coconut tree. Amazing how alike this process is to mammal reproduction, where the womb holds and feeds the embryo.
This one is well on the way, so the bubble has almost filled the hard shell, while the roots haven't got going just yet. Much of the coconut flesh is still there. Give it time.
Now, if you can catch a coconut that hasn't quite reached this stage (where the bubble gets a little bit spongy) then you get this, and it's delicious.
It tastes like a sort of coconut marshmallow, juicy, fresh and sweet.