Ugh. Now I never want to go to the friggin zoo again. That was creepy right from the start- something about your descriptions made the setting seem extra spooky even without the tree. I liked the characters- even in a one-shot, you managed to make characters that the reader can actually care about...I was like "NO!" when Mark died.
So, great job. The whole thing- especially the part where they're both crawling- had a distinctly nightmarish feel to it. Which I suppose is just what horror's about.
That was a great read! What an original premise, I'd never read a horror story like that before! It's always nice to find something new and fresh to read, since so much of horror is cliche it's a hard genre to be origional in. But you did it! I'll have to read your other stuff now. Keep up the good work!