Remember that a magnet holds onto all pieces of ferrous metal, even small sharp ones that are not easily seen.
Today I was working in the shop and had a magnet on top of the anvil. It was in the way so I reached over to shove it out of the way. Lo and behold, there was a very small sliver of razor sharp metal there.
I got a nasty, dirty, deep slice across the heel of my hand. I won't soon forget that lesson, learned the hard way.