Unfortunately Mri'Thas is taken by surprise by the gnome's sudden disappearance, and by the time he thinks to mark the spot he's already looked away.
Callen, however, immediately stops and listens, trying to pick out movement. He hears a whispery touch of leaves and a slight scrape of sandal on the ground, as if someone is edging through the trees... a grunt of painful breath... there is a sudden crackling crash, audible to all, as one of the tree branches abruptly snaps... and then a thud as something hits the ground. Blood begins to trickle out from somewhere unseen, and as Callen watches the gnome's body slowly fades into view, exactly where he'd predicted it would be.