It gets even dumber when you notice that Oda gave the sandworm a cross-shaped mouth similar to the original Dune sandworm design from Heretics and the David Lynch movie (but with four jaw-like "mandibles" instead of three) but Peter's sandworm form still opens its mouth as though it had a human mouth with human lips.
Instead of the mouth opening in four directions, sort of like this.
↓
But less detailed obviously.