In this passage, the man's reaction can best be described as
reckless
Read the passage from Part 1 of "To Build a Fire."
Once, coming around a bend, he shied abruptly, like a
startled horse, curved away from the place where he
had been walking, and retreated several paces back
along the trail. The creek he knew was frozen clear to
the bottom-no creek could contain water in that arctic
winter-but he knew also that there were springs that
bubbled out from the hillsides and ran along under the
snow and on top the ice of the creek.
enthusiastic
sympathetic
cautious