Things went all wrong at some point. We were walking up endless switchbacks, but then the naval captain with us stops short and lies down in the middle of the trail—as we'd done a zillion times before on the trek—but this time he’s dry heaving, shaking. We were blindsided because this guy's done tours in Iraq, but he was challenging himself on this trip, too, to forage (read: eat only what he could find and kill on the trail) with Coyne.

They hadn't killed much, though, because it's illegal in national parks, so they were running on black elderberries, mice, and yarrow. That, plus the nine hours hiking each day and the elevation, were too rich for his blood. Luckily, Coyne knew what to do (again: it’s crucial to have an expert on hand), and got him stabilized with electrolytes. The takeaway, though: Sometimes things go wrong, so be aware of warning signs and treat them seriously.

NEXT: No Turning Back