Rhamses: You say that you didn't cause all this. You say this is not your fault. So let's just see who's more effective at killing: You or me.
When they come over the mountain, Moses looks out at the Red Sea and sees nothing on the horizon. When they get across, they can see the mountains where they crossed very easily - the area on other side has mountains similar to the ones they crossed, which should have been visible when first approaching.