Watson runs into Stapleton the naturalist as he is taking a walk, and Stapleton invites him to come with him to his own home, Merripit House. As they do so, they are surrounded by the geography of the moors. The atmosphere is ominous and eerie, and the moors are portrayed as a threatening, isolated, and dangerous place.
This atmosphere is amplified by Stapleton's talk of the moors. He says he knows them very well, for traversing their more dangerous parts allows him to arrive at isolated places where he can catch rare butterflies and insects. He describes the dangerous bogs, or what we might call quicksand, which horses disappear into, never to be seen again. The two men hear the cry of such a disappearing horse as they walk.
They also hear an unnerving sound that Stapleton thinks is the hound of the Baskervilles lurking nearby. Watson describes the sound as a "low moan, indescribably sad." Stapleton calls the moor a "queer" and "uncanny" place. Watson gets increasingly spooked and uneasy as they walk across it, stating,
I looked round, with a chill of fear in my heart, at the huge swelling plain, mottled with the green patches of rushes. Nothing stirred over the vast expanse save a pair of ravens, which croaked loudly from a tor behind us.
Although it is not night, this a gothic setting, one that raises the reader's anxiety. It is easy to understand how this setting could lead a person to believe the supernatural stories about the hound.