Only bit 0 is used. When it is set, the giant crab ("A giant crab", the first byte of Table_FollowingItems) follows the player from room to room. ChangeRoom sets the bit at EF91 when the player walks into The Rockpool while the crab is there, and clears it at EF64 on reaching The Rocky Path. Action_Shout clears it at Shout_Crab when the boulder falls on the crab. Bits 1-7 are never set. MovePlayerToRoom moves the item for each set bit into the room the player just entered.