Knowledge is power. That's what happened there. Emily knew that the mother snake or its relatives would follow them because of that loud voice that Leo just made. She knew she wasn't supposed to make any sound. From here at that moment they had to leave the tunnel immediately and immediately. It's that event that should end immediately. They should have survived. Emily didn't have the luxury of time to wonder why this handsome guy is standing here in the tunnel with her. She doesn't know anything about it and she won't ask.
They knew the hole that passed them to the roof was too close. That's because of one thing. It's the air that gets lighter. The bad, bad air in the tunnel is about to end. It's starting to disappear. Instead, there's more fresh air. The air comes from outside as if the snow had fallen. Very cold and beautifully refreshing. Even if he's not pretty, he's in better shape than they're in.