Mystery Solved?

Well perhaps partially solved! Ever since I posted a piece on mussel eating Oystercatchers, I've had a slight worry that, perhaps, that wasn't the entire truth. Certainly, at times I've seen them chisel away at the mussels, but that wasn't what my recent observations on them suggested. While photographing some Sooty Oystercatchers this morning, I 'shot' one with something in its' bill. On putting the image into the edit programme and enlarging it (see pic), I realised it was a small crab. Any fisherman using mussels for bait, would know that each mussel contains a small crab--I assume it spends its' entire life in the shell (perhaps someone could enlighten me)--and that would appear to be what the Oystercatchers are after,( although it is also possible there may be small crabs secreted among the mussels). There would appear to be some advantage to the Oystercatcher to feed in the wash (see pic), as at that time the mussels open, and allow a smart bird to gain access to the crab. I'm sure that's not all their feeding on-- better keep watching!