From the same school of thought as, "Hey GM, which book did I just randomly pull from the shelf of the wizards' library?" No plot hooks here, just flavor additions.
Found, normally, deep in the swamp, the Friar's Weed's poison is something to be watched for.
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.