I have seen on many occasions, larger shorebirds with long beaks, flex their beak tips. It was surprising, but in a way it made sense with a long beak. Sort of like the old days in the general store when the grocer would grab a can from a high shelf with a long stick bearing a forceps at the end. I never figured that smaller shorebirds could do it, too. This sanderling can. Why? Maybe it's a good way to keep from getting a mouthful of sand when your beak touches a buried prey item.