Once upon a Christmas, a puzzle

My mom is a retired math teacher.  She taught in jr high (yes, she is a saint) and in high school for what seemed like forever before she retired several years ago.  She was a good and caring teacher, always staying in at lunch to help a struggling student, taking calls at home from kids who had homework questions, and so forth. 

My mom also LOVES (understatement) puzzles, and she often felt generous around the end of the semester.  She wanted to give those kids who needed help the opportunity to raise their grades.  It wasn't to be an easy task by any means, but something that was math related and required a LOT of patience and logic.  Mom loves thinking outside of the box stuff.

One year before Christmas, she found a puzzle, in the fabulous Games Magazine, called "Oh, Deer!"  Not just any puzzle, but one that met all of her requirements.  She handed it out to the whole class as extra credit, and waited to see what happened.  I remember it all quite well, as I was in high school at the time.  It took some kids days to puzzle it out, but since they wanted the extra points, and they loved the puzzle/challenges my mom gave them, a fair portion of her kids at least tried it out.

My mom then got a crazy, twisted idea: give the puzzle to her own children, have them solve it before opening their gifts.  Most of the 6 of us completed it, we're all puzzle freaks too :)  The only downside was that dad found out about it Christmas morning, and he wanted to work out the puzzle before we opened gifts too.  We revolted and our gifts were doled out properly, and afterwards dad locked himself away in the office to work out the puzzle himself.  He came out several hours later, puzzle solved, and quite pleased with himself.

Every year, I think about that puzzle.  And this year I've finally found it again.  I'm thinking it will become a new tradition here as well.  You're welcome to try it out, but be warned, it's not as easy as you think.  The puzzle can be found here.  And the solution is here.