After the carnage in the woods, and killing a wild pig, Rambo is shown 'scoping' his surroundings, before entering the deserted mine. In the background (and also at other times), crickets or cicadas can be heard, and yet there's snow on the ground, and the opening sequence shows a 'Merry Christmas' garland hanging in the Sheriff's office. Crickets would be long dead by the turn of the year.