Mary drank the bottle enough to become a centaur. She waited a few moments and then felt a sensation below her waist. There was a bulge in her pants which must have been the tail. Her skirt has about to rip until she was able to take it off. A majestic brown tail came out and was about 2 feet long.
She then felt a lot of prickling on her legs and saw tiny brown hairs growing all over her legs. Soon everything from her legs to waist was covered in hair. Then her feet started to feel weird. Her feet were getting smaller, and harder. There were no hair on her feet as they started to get smaller and become black. They were now hooves which made walking for Mary weird.
The transformation stopped for a moment but then started again. Her butt was now getting bigger or longer as 2 little things started growing from the bottom. Mary realized this was probably the part where the -taur part kicked in. Mary tried to find a mirror to see the transformation better but the weight she was gaining wouldn't let her.
The 2 little things were now legs of a horse which were about a foot long by now while her waist still stretched backward. Mary tried to stand with these feet but they weren't strong enough yet. For now she had to stand with only 2 legs. Her legs were becoming more horse-like so she couldn't stand up, forcing her to lay on her couch which was barely big enough to support her. She realized this will be helpful in the future.
She was completely done with her transformation now. She also noticed that her ears were like a horses. She got up and was able to stay up easily. She took a couple steps and found it easy too. But then she felt something, something growing!
Mary couldn't see what it was because of the new part of her body in the way. She could only tell it was somewhere near her groin, and it was big! She took the vial she drank from and it said at the bottom "MALE". she knew what this meant and had to do something quick!