Tried out the finger version with three glasses of water. I could only reproduce it partway - my middle finger felt like it was in hot water, when it was actually in cold.
I'm starting to think this whole concept is bogus or at least very variable across people.
> for some people the brain is tricked into thinking the middle finger is in the warm water
It worked for both me and another willing participant, but we found it depended on the orientations of our fingers.