00:00If you walk across the exact same line in your yard every day,
00:05Your feet slowly crush the grass and compact the soil,
00:09Causing the strip to turn bare and hard over time.
00:13Now when it rains, water can't soak in as easily,
00:16so it starts flowing along the groove instead.
00:20Each storm scrapes a little more soil away, causing the groove to grow deeper.
00:25And if you walk back and forth for several decades,
00:29while the conditions are just right,
00:31that small groove could turn into a six-foot-deep trench perfect for war.
