Yes, indeed, this is how Saruman communicated with Mordor. That’s clear now, right? Gandalf had thought to test the stone out for himself, but was saved from that ordeal by Pippin so eagerly taking it upon himself. Bad things could have happened if Gandalf became revealed to Sauron, so…thanks?
Gandalf finds a way to take this advantage. Sauron probably thinks that Pippin (who must have the ring) is at Isengard. He’ll focus his attention there until he learns of its downfall. For now, Gandalf will take the time he can to ride ahead with Pippin. Théoden and his men, meanwhile, must ride with all speed to Helm’s Deep.
Suddenly, a dark winged shape passes over the moon. Time to go!
Aha! Look! A reason that this scene takes place outside! It doesn’t seem to notice everyone huddled on the ground, but a Nazgûl casually flies by. You can’t do that inside Meduseld at Edoras. Take that, film interpretation!
Didn’t I mention the other day that there would be some advantages to be gleaned from this situation? Well, here you go. If Sauron is focused on trying to pry the ring off Saruman, he won’t be looking for it to come from somewhere else. Especially not from two dudes just walking into Mordor. As you may know, you can’t just simply do that. As if it already wasn’t unlikely, it’s more unexpected if Sauron thinks that the ring is somewhere completely different.
It’s all going to work out just fine. As long as Pippin stops doing stupid things.
“‘Let not the swift wait for the slow! Ride!'”