It's possibly a good thing, then, that neither of those with her were in a hurry to jump down a hole - Regulus, because he wants to watch first out of suspicion it could be a trick. And, Mikoto, because she wants to watch and see how it works.

So both are peering down the shaft when the Andalite reaches it. They quickly pull back, staying close to walls and out of the way, in case he's headed for the floor they're on.