Sarah

Sarah Fletcher, aka The Exterminator, is Aperture's resident pest control. As far as Aperture's animal population is concerned, she's one of the most terrifying things they hope to never come across.

Method
Fletcher practices an unusual but highly-effective method of dealing with birds, rodents, and other creatures that manage to get loose in Aperture. Instead of outright euthenizing the pests, she captures them and returns them to her workshop. The front of her workshop and living space is filled with cages and traps of all kinds, but no human being has ever set foot inside the back rooms aside from Fletcher herself, ensuring her work remains a closely-guarded secret. Even the Genetics department shudder to imagine what The Exterminator does to the critters she catches.

In reality, she has never killed a single creature. Instead, Fletcher has a remarkable talent for haberdashery and tailoring, as well as a particular interest in photography and film. After being fitted into a cute array of outfits and photographed and filmed repeatedly, she releases the creatures she catches. Her method of extermination is to ensure that the creatures 'die from embarrassment', and never shows its face in Aperture ever again.

Laika and Polaris
Despite the treatment, there are still some animals which flock to her - either as a result of Stockholm Syndrome, or out of genuine affection - including a dark-brown rat she has named Laika. Laika was 'married' to Polaris in a lavish ceremony, though Polaris refuses to recognize the marriage as binding due to the trauma of being forced into a tailor-made tuxedo with bowtie and tophat. Laika's affection for Polaris is undiminished, despite his obvious dislike of her (going so far as to refuse to call her by name, adopting instead the nickname Sponge Thief).