Mary found a vial with a picture of a cat. She remembered how much cats like milk, and chuckled. She drank about a quarter of the vial and then placed it back in the box. Her head felt dizzy again, but it wasn't enough to knock her out completely this time.
She felt her upper body tingle. As she looked closely at her arms, she saw light orange fur growing from her skin. Within minutes, the fur had covered her body above her waist, preserving the black and white cow fur on her legs. Her ears expanded and migrated to the top of her head. They became pointed and furry. Her hair changed to an orange color as well, growing slightly longer and thickened into a less controlled mane. Her teeth sharpened into fangs as her tongue became very rough. Her pink nose flattened and pushed out from her face while white whiskers emerged from her cheeks and above her now yellow eyes. Her fingers shortened and grew retractable claws. The skin on her palms thickened to form soft pads.
"Mmm..." she purred. She flexed her fingers, which were still relatively dexterous and able to work as well as a human's. Her ears could now pick up distant sounds such as the air flowing from the floor vents and the faint hum of electrical wires. New smells entered her nostrils, one of which was milk. She looked down at her udder to discover the white liquid seeping slowly from her teats. She absent-mindedly licked her furry muzzle.
She rummaged through the kitchen and found a large mixing bowl. She positioned herself over the bowl on the floor and grabbed a teat with one paw. She pulled hard, feeling the milk squirt out of her. The force of it excited her, and she quickly pumped milk into the bowl.
Once it was full, she began to lap it up, not bothering to pour it into a cup. The creamy liquid was warm going down her throat and she purred happily. She finished off the bowl and laid down on the floor by the window to bask in the sunlight. Her udder no longer felt painfully full, and her stomach no longer felt painfully empty. Mary had found the perfect double-form.
The only question now was what to do next? She couldn't live the rest of her life like this, but she didn't want to change back either. She shrugged off the thought, deciding to enjoy the day off with her new body.