fun concept but...

The idea itself is fairly interesting letting people decide what happens through the story but I think the way this was done is going to catch a good deal of crap. For one its just one annoying loop (those are always annoying) offer an end with the "what should it say" and a reply button if they didn't grasp what happen in the 12 or so seconds of animation. Over all I would re-think the way you go about this project and come back, people will be a lot less likely to flame or down your submission if it does not cause their eye to twitch a little with that loop of animation and sound.

hmmm

the letter explodes, thus killing the knight, the bird, and the tree. your welcome

hmm...

How about this: The message is a royal decree stating that the king wants toilet paper made of silk, and he has to go off on some comedic quest to find it. (I'm suggesting a non violent alternative to the ones below, in case you didn't want violence.)

Anyway, I'd give this an eight because the idea of your reviewers creating the end is a nice change of pace. Your artwork is decent and the music fits the mood. I wish you luck on your creative journey.

hmm

he can't read the letter properly so he puts on glasses then holds it close to his face
the letter suddenly explodes blowing his head off his body
skip to a scene of the bird picking out one of his eyes

Story idea

man gets stuck in endless loop of time in which he walks to a tree wearing a suit of armor and recieves a letter from a bird.....
Oh wait =3