We apologize if this is a bit confusing. Basically, we wanted to show that each move of the crab was a single move. To move the crab "2 hexes", you have to think of it as a "waddle" in two separate movements.  

The crab head and both pincers should be touching each other at all times. I.e., if you think of it like a clock, the crab head is at the center, and the pincers are attached at 10 and 2.

Since the crab is always attached to its pincers, even during movement, it "waddles" from side to side.. Therefore, if the crab's target is 4 hexes straight ahead, it is going to take an indirect path to get there by twisting back and forth. To do this, move a pincer and the head forward while staying attached to the other pincer. Then, move the second pincer and the head in the same way.

Since the crab is always headed for a Champion, it should not find itself stuck on a wall where both pincers are touching it (thus not allowing you to advance by moving a pincer and the head). The card states that the crab ignores footholds, so those won't trip it up either.