A short alternate ending to Portal. Rated T to be safe.
She had not expected the fire trap to fail. She had not expected the subject to scurry away into the deeper parts of the facility. Even now She could feel her feet pounding through Her beautiful facility, her pride rippling off of her in vile waves. She thought she had won. She knew better.
There had been another rat in the backworks once, She remembered. He had been clever, that one, so clever that She had considered sparing him and using him as a test subject. But, try as She might, She could not formulate the medication that would make him sane, make him usable. She had no use for such a volatile subject, however, and he couldn't hide forever. His body had joined his beloved Companion Cubes in the incinerator long ago.
The only signs of his existence that She could not erase were his infernal cubbyholes, his dens, as he had called them, before he had finally lost the power of coherent speech. The dens, and the paintings inside of them, remained untouched, a dash of color in the pristine white environment She had created. They aggravated Her. Clearly the rat had formed his dens so near the testing tracks just to spite Her, a feeble show of resistance. She did not yield, though, did not yield to the senseless rage that he intended to form in Her. She knew that he would be trapped. Eventually.
She did not understand, though, why the subject reacted so strangely to the dens. Clearly, she should have reviled them for interrupting, no, damaging the perfect testing tracks. Instead, she ran to them, hid in their confines, ran her fingers along the murals that could be barely picked up by Her cameras, whispered the inky words, The cake is a lie. The rats were wrong, both of them. The cake was real; She just did not give any to the rats who misbehaved. They should have known better.
However, Her disgust with her subject's-well, rattiness, didn't stop Her artificial processors from running. She recognized the trust she placed in those splatters of paint; She realized how unthinkingly the subject obeyed them. And while She was unable to tamper too much with anything near the testing tracks-the scientists who built Her had seen to that-She could do as She liked to the inner workings of Her beloved facilities. It wasn't hard to use the robots She had begun to build for testing as painters. They hardly needed fine motor skills to imitate the first rat's work.
So, yes, she was drawing closer to Her chamber. Yes, she was equipped with the finest piece of equipment to ever grace the earth. But She still held all the cards. She knew beforehand the path that the subject would take. It would take her to Her chamber, but also to her death.
With every step she took, every move she made, every second she spent scurrying about the machinery, Her chamber filled ever more with neurotoxin. Even as she ran down the hall towards the closed door where She resided, the chamber reached neurotoxin capacity. Even as she stood just in front of the door, the neurotoxin concentration was enough to drop her in a moment.
She never expected Her first trap to fail.
But there's more than one way to catch a rat.