Stacy was a star cheerleader, and Tom had often referred to her thighs as "drumsticks". This prompted a series of poultry-based nicknames set around her being a chicken, and the eventual Halloween costume of her dressing as one, whilst Tom was colonel Sanders of KFC fame.
Now, he thought, it might be an idea to transform her into an actual chicken. He purchased a vial of chicken transformation liquid illegally, which he then slipped into a glass of water offered to her at his house...