Charlie, quite ill advisedly, raised her wand with a determined look on her face, thinking to send some aggressive sparks at the older students.  She wasn't sure what might come out of her wand without knowing any spells, and what happened shocked her as much as anyone else.  

One of the compartment doors suddenly exploded outward, striking one of the older students, knocking him to the ground.  

"Ha ha!" she cried out, "Take that!"