Book with a green hand on the cover

[jamisnively]

My sister swears she remembers me reading a book when I was late elementary school age, around 2001-2004ish, and she thought it was a Harry Potter book. But none of the Harry Potter book covers match her memory of the cover art of this particular book. I have vague memory of what she’s describing, a green hand that comes out from the bottom of the picture and you don’t really see any other part of the body the hand comes from. I don’t remember what the plot might be, but it would be a book written for children. Anyone have any idea?