I'm sorry.... call me a "Nay Sayer" but the pics just don't fit with the story in my opinion... Think about it... Cleaning a fireplace mantle, nearly all mantles i've seen are about chest high. That'd put your arm roughly 90 degrees, straight out in front of you. this wound is obviously a slice from top to bottom or bottom to top which would place the arm up in the air, or down at your side... assuming your arm was horizontal and the knife came down vertical, it would be a small stab wound, not an 8 inch long 2 inch deep slice. If this story is truly what happened, then the cut most probably would have started on the left side of forearm, traveled through a ways and ended on the right side... Also, I don't know how well you react, but i have had some very close calls... Accidents within inches from me, just waiting to happen. I've avoided many a close call by instinctive reactions alone. IE, you know there is a knife hanging from the wall, you are 1 foot away from the wall and the knife is 4 feet above you. Undoubtedly, you SAW THE KNIFE FALL, unless you were not paying attention to what you were cleaning. 4 feet in height + 1 foot in distance = plenty of time to get out of the way. Common sense points to real picture with fake story! However, if you were to post some recent pics after you fully healed, I'd be much more inclined to believe you.
Be more than happy to there CSI guy!! Would you like to see the knife too???
Shit. Glad it wasn't one of your kids. That is one sharp knife there. Shame you aren't as sharp and didn't hang the bloody thing better. Thanks for sharing the pics.