"The Handicapped" is a science fiction short story written in 1967 by Larry Niven, set in the Known Space universe. The story introduces the Grogs; the sessile but sentient inhabitants of the planet known as Down.
Mr Garvey arrives at the planet Down, having heard about the natives called Grogs. Garvey Limited, a company owned by his father, makes artificial limbs and other tools for the "Handicapped" species; sentient beings that evolved minds but with nothing that would serve as hands, like dolphins. A local reluctantly agrees to show him a living Grog in the desert, but the Grog turns out to be a disappointment. It is sessile enough, being a furry cone living anchored to a rock, but it seems utterly void of sentience. The latter observation is later confirmed by a local exobiologist.
The next morning, Garvey has a revelation. Somehow he knows the Grogs are sentient, without knowing why he knows. He returns to the desert and finds another Grog that begins to communicate with Garvey telepathically. It turns out the Grogs are indeed sentient beings with strong telepathic abilities, but for fear of being perceived as a threat for this very reason, they have concealed this until now. But having read Garvey's mind, and seeing that he can help them break their isolation, they are willing to take their chances.