Thanks 
The first point I noticed show hot on the thermal camera was a point in front of the vice-grip where the nickel strip touched but weren’t well connected. The nickel strip were definitely offering significant resistance because of it was only 0.15mm thick. That resistance could probably be roughly calculated, but I didn’t bother.
A boom would have made a more exciting video, but no-boom is also good to help us understand what the batteries can handle.
The resistance of the nickel strips increases with temperature too.
What you want to do if you’re after dramatic effects 
is use a short thick copper strip and clamp it in a vise.
Oh, and then run away… 
I’m not sure that would even do it with this battery, it has very low internal resistance. That would definitely get more amps flowing, but without the 400F nickel strip dumping heat into the cell it might be end up heating to about the same temperature. idk.
It’s a matter of Ohm’s law.
the lower the external resistance, the more will be turned into heat by the internal resistance.
And overall, the total resistance will be much lower too, so more current will flow, increasing the total heat generated, but 90% or more (this of course depends on the length, width and thickness of the copper strip) will be generated inside the battery.
Another possibility though, is that the battery has a thermal fuse of some sorts, which will disconnect the battery.
That’s no fun. 