Years ago in an old circle saw mill I worked in we found the tip of a pole saw blade in a white pine knot. Guess someone was limbing the trees up for better value and broke his blade off. Luckily it didnt mess things up much. With a saw Ive found tons of concrete, RR spikes, and my favorite was an old time hinge for a gate. That was fun getting out. I am yet to find a horse shoe burried completely in a tree.