They can only be unstuck when one of the dies. When the clump attacks, each Pixie in the clump attempts to attack in the same direction. An important exception to this rule is the case that a clump has already spent its attack for this turn, and then a new Pixie joins the clump. The segments form a chain, each connected to the next. Each tail segment must move into the hex vacated by the segment in front of it.
All segments move simultaneously.
The Head can attack, tail segments cannot attack. The Head can attack any adjacent enemy creature, just like any creature can, and it has a number of attack dice equal to the number of segments in the whole Carrion Crawler, counting the Head itself. If there was another segment following behind the destroyed segment, then the following segment becomes a new Head. This implies that every 3 contiguous segments in the whole Crawler form a 60 degree angle. They can eat only one corpse per movement phase.