sometimes that does just happen.
My friend shot a bull elk with his 338 whizbang mag and then, contrary to what you'd expect from watching any TV hunting show: it ran into the woods.
We and another friend found the blood trail and followed it for 40 mins and it just got fainter and fainter until it just stopped. We 3 circled for hours trying to refind the trail and couldn't. I seriously hoped that the trail disappeared b/c the elk had a flesh wound that had closed rather than a gut shot, but no way to tell. It just makes you sick when you hit one and lose it.
I'm right about the metric system 3/4 of the time.