Yes Walter, no shit. But Peter does not have time to facepalm about Walter being Walter. They're running flat out together now, and Peter doesn't know if it's going to be enough. As they reach the first opening, he pushes Walter in front of him, hard, and dives in himself just as the worm slams into the rock, unable to follow through the narrow opening. The cave shudders and some debris falls on them from the ceiling, but it holds. For now.