I saw the video. How sure are you it is part of the foot? if it is it shall come stright from the center base of the clam if not you shall see parts of it attached to the shell somehow. If you see it is directly attached to the shell then remove it whatever it is. If in reality is part of the foot you have two options, leave it as is and wait it out and see how it reacts, if it grows or develops some brown gelly or you may take some sharp scisors and cleanly cut about 3/4 of it, if it is part of the foot the clam shall grow a new one.