"Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying." -- Arthur C. Clark
The gnome hefts the giant tome situated on his back and then pushes his round spectacles up his protruding nose. He rubs the tip of his nose, knowing that he should really stop studying with his face so close to the books. The skin would sometimes rub off the tip during long hours of recording and study. Specks were moving on down the road, and he produces a spyglass from a loop on his hip. Through the lens, he spots a group of adventurers. He grins from ear-to-ear and gives a hoot, almost losing his balance due to the weight of the book on his back.
"These fellows look like they have purpose! It's time to find out what they're up to!"
If a creature is transformed into another creature (say, a human into a dog), then that creature will become more and more accustomed to the new form until a point is reached where reversing the spell is impossible. A second transformation is possible, but the creature will have to go through the whole process again.