Knocking in Allegheny County, Pennsylvania

A friend and I were sitting down on a pipeline right of way. We heard a noise that sounded like something that a large bird might make. A little while later, we heard something that sounded like someone knocking on a tree with a piece of wood or something. These sounds continued alternating, off and on for about 20 minutes or so. I remember that my friend and I were talking about how the sounds were a little strange, and getting louder. At one point, I realized that the sounds were coming from a point very close to us, and they seemed to be coming from the same place, so we stood up to see if we could see anything. It was then that we saw the animal. It looked at us, we looked at it, and we all took off running. Before running, I noticed that what I was looking at was about 7 feet tall, relatively the same proportions as a normal human, except for longer arms, and it was covered with shaggy (2-4" long) grey hair. The face was not clear to me. I have slight astigmatism and I could not make out the features at the distance of about 20-30 yards. The animal crashed through the woods as it ran away- just breaking down everything in it's way. I kept looking back as I ran, and it just seemed to be going in a straight path up the hill towards Sample Road. Some years later I visited a wax museum in Niagara Falls and at the end of the exhibit was somebody's idea of a bigfoot. It looked very much like the one that I saw, except for the facial features. This one had big pointy teeth and looked pretty angry. I could not clearly see the face of the one I saw, but I don't think it had big pointy teeth and an angry expression.