From the story archive · Fictional encounter
Deep in Mammoth Cave with a tour group. Guide turns off all lights to demonstrate "true darkness." Thirty people standing in absolute silence and pitch black when—FRRRP—a barking spider echoes through the ancient cavern.
The guide flips the lights back on and says completely deadpan, "And that, folks, is the famous Mammoth Cave Barking Spider—a sound heard by explorers since the 1800s." Most geological barking spider moment ever.