So before I started any real quests, I just went around exploring skyrim, going into random caves and such. I happened to pass by a place that I thought was called Greenspring Hollow (A little west of whiterun) and a sabre cat jumped out and started mauling me so i killed it and just went on doing my thing. The next day I joined the companions and did a few quests for them, one was "Animal Extermination" it turns out I was supposed to go to Greenspring Hollow and kill a sabre cat. When I got to the hollow, the quest objective was right above the already dead sabre cat's corpse. There was absolutely nothing I could do, I tried to reanimate it and kill it again, but it just turned into ashes and nothing else changed. I tried going back to the questgiver the companions huntress, and she just told me to go and finish the quest she'd already given me.

Just a warning to people that haven't started the companions yet, stay away from Greenspring Hollow.

Anybody else have this happen to them?

I haven't had this happen yet, but if you run across any rare books, or any kind of musical instrument at all, DON'T PICK IT UP. That will screw future quests for the College of Winterhold and Bard's College.