Morgana,
The knife went flying and wound up in the brush at the fringe of the clearing. It was the underbrush that caused it to stand upright and also concealed its presence from Clark. I personally have had an errant knife land in just that manner when practicing my throwing technique (and missed the stick) so it can and does happen. Not often, admittedly, but enough that this was a legitimate scenario. I would not have used it otherwise.
