People on mountaintops will see it sweeping across the landscape, a cloak of darkness careening in their direction at more than 2000 miles per hour. This is the moon's innermost and darkest shadow, the umbra. Mabel Loomis Todd, a 19th-century eclipse writer, described it "like a wall, swift as imagination, silent as doom."
Things will get weird, and fast. The chirp of crickets may replace that of birds. Fireflies may emerge; bats may flit. Cows may low and jangle back to the barnyard. Pigs may wallow, flowers close. Chickens may return to roost or—as happened when an eclipse passed over Easter Island in 2010—freeze in place, standing flamingo-like on one leg.
A gust may sweep across your face as the wind shifts direction. Even here in August, you may shiver as the temperature sinks 10 degrees. Anybody who brought telescopes or binoculars that aren't filled with nitrogen may be disappointed as the plunge causes lenses to fog.