Where does Susie say that an icicle is the perfect murder weapon?

It's summertime in chapter 10 of The Lovely Bones. Ruth, Samuel, and Lindsay are attending the statewide Gifted Symposium, a retreat for bright children from the seventh, eighth, and ninth grades. In the last week of the symposium, a competition for the children is announced. The precise details of the competition have not been revealed, but the children know that it will involve the construction of a better mousetrap. However, at the last minute, there's a change of theme. Fliers posted all over the camp announce the competition's new title: "CAN YOU GET AWAY WITH CRIME? HOW TO COMMIT THE PERFECT MURDER."
Up in heaven, Susie and the other spirits regularly play a game based on this very theme. Susie always chooses an icicle as a murder weapon because it will quickly melt away once it's been used.