Reality test
The Rat turns ordinary social interaction into an experiment. The narrator and Rat play the Game: ask strangers about the Rat and discover whether another person will acknowledge him. The suspense is ontological but the procedure is embarrassingly mundane—talk to somebody at a bar.
Mutable companion
The Rat can appear with Cold War spy / counterspook styling and behaves less like a stable animal character than a companion whose reality is continuously renegotiated through attention.
Why he matters
The Rat anticipates several later corpus structures: naming as a way of making something socially operative, consensus reality, and the use of another person’s response as part of the artwork.