Fred hadn't meant to scream because screaming could be a very bad thing; it could have caught her in more trouble than she found herself in. Well, she wasn't in that much trouble. She'd just scared herself, thinking too much.
She'd been walking, trying to be careful and aware. Perhaps she was a little too aware. She tripped over something along the way, and as she was getting up, she felt something touch her. She let out a bit of a scream, before laughing. She hadn't been grabbed by something that wanted to eat her brains. The branch wasn't a hand, but darned if it didn't feel like one.
She laughed softly at herself as she freed her foot and stood. She would have considered laughing more when she heard something coming her way. Yes, that was what she got for screaming.