"Simply by calling the rock a “pet”, Gary got people to treat it as a living creature with feelings, desires and needs of its own."
In his discussion of human psychology at Kindle location 832, Gregg uses Dahl's Pet Rock to illustrate how people can knowingly treat an inanimate object as if it possesses mental states. His description of this participation as semi-ironic directly supports the manuscript's wording about treating the rock as a living thing.
View Source