Near the end of Mrs. Frisby and the Rats of NIMH, Mrs. Frisby overhears a conversation in the Fitzgibbons' farmhouse. Mr. Fitzgibbons, the farmer, tells his family a story about how a local hardware store owner claimed to have caught several rats in the act of stealing a large...
Near the end of Mrs. Frisby and the Rats of NIMH, Mrs. Frisby overhears a conversation in the Fitzgibbons' farmhouse. Mr. Fitzgibbons, the farmer, tells his family a story about how a local hardware store owner claimed to have caught several rats in the act of stealing a large motor. While Mr. Fitzgibbons doesn't believe a word of it, he does jump on an offer from an exterminator, who offers to come clear the rat colony out of the farm's rosebush for free.
Unbeknownst to Mr. Fitzgibbons, the rats who live in the rosebush are highly intelligent rats who have escaped from a laboratory called NIMH.
When Mrs. Frisby informs the rats that the exterminator is coming, the rats guess that the "exterminator" (who also heard the motor story) is actually a NIMH operative come to recapture them. Fortunately, the rats have already been working on a plan to move their colony from the roots of the rosebush out to Thorn Valley, where they've set up a self-sustaining farm.
To fool the exterminator, the rats trash the rosebush colony, making it look like a pile of ordinary garbage similar to any rats' nest. Ten of the rats also stay behind so that the exterminator will believe he actually cleaned out an active rats' nest, instead of becoming suspicious that the rats Mr. Fitzgibbons complained of are suddenly gone.
The exterminator pumps the rat colony under the rosebush full of poisonous gas. Two of the rats are killed, but the rest escape through a back exit.
From the exterminator's point of view, the rat tunnels under the rosebush probably looked like any other rat's nest during extermination: A lot of junk and a few dead rats. It's possible that, if he had looked closely, the exterminator would have noticed that the junk contained a lot more mechanical and electrical parts and documents than ordinary rat-nest junk—but the novel never tells us whether the exterminator looked closely or just assumed it was an ordinary nest of rats.