Around an active volcano, you can feel its gurgles inside of you. It's an unsettling feeling we are more used to than we even realize. It's infrasound. It's how the Chinese 3,000 miles away from Krakatoa felt its eruption. Its slow but powerful sounds travel further than regular sound.

Infrasound floods our cities and is felt with every airplane passing overhead.

What else travels slowly but surely—besides the tortoise?

I travel slowly, but powerfully.

Infrasound sometimes referred to as low status sound, describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear is the primary organ for sensing low sound, but at higher intensities it is possible to feel infrasound vibrations in various parts of the body. - Wikipedia‍