Cant really tell from the picture, but it may be regurgitating its food. If the food is too big, improper for the species, or it only digested the part of the food, etc., it may spit it back out. Like if it digested shrimp, it might spit out the shell.
I wouldnt try to pull it out though, let the anemone do it on its own and then pick up the "sack" and throw it out. (IMO)