[@Spriggs27]
Because Vesta is his master and he only pranks her for his own enjoyment. She won't be the only person he plays around with either, everyone in that house is fair game to Avery right now. Zin. Orgus. Hell even Aya if he felt like it.
EDIT: This is Avery's ultimate goal to make everyone do now:
[youtube]https://www.youtube.com/watch?v=HhVi3Ls7KtU[/youtube]