Violet was feeling quite bored, she didn't really have much to do. She was having one of her off days - feeling a little bored, lonely, and miserable.
Without realising where she was going, she ended up in the garden, and saw, not too far away, a group of people she knew practicing for Defence Against the Dark Arts.
A smile crept over Violet's face. Aha, she thought. Here's something to allievate my boredom!
She concealed herself behind some bushes, so nobody could see her. They didn't look in her direction, anyway.
Violet pulled out her wand, and bit her lip to stop herself from laughing. With a twinkle in her eye, she pointed her wand at Jolly through a gap in the bushes and whispered, "expelliarmus!"