and if you watch closely, the metal is actually parting well ahead of the cutting edge in most of the clips. like in your screen capture still, you can see the metal coming apart well before making actual contact with the tool.
Yes, a very viscous liquid and a good thing too or we'd have to vanquish terrorists with stone tipped weapons. The graver tip looks like the prow of a icebreaker and the metal much like ice. What I thought was really wild is the welding of debris under the graver I wonder what the temperature is at the local molecular level.
Wow, thanks, Mitch. This explains a lot about porpoising, why chips sometimes break off at unexpected times, etc. I'll have to remember this the next time unexpected things happen in my cutting!!!