There are tons of things I had never considered about how difficult it is to fool your brain into thinking it's touching something it's not. I think the most important technical issue to overcome is timing. Much like how your brain can understand hearing someone's voice AFTER seeing their lips move, but not the opposite... the lag time of the sense of touch is an important thing for your brain. Another thing I hand't considered is the "rise time" that has to do with internal stresses in your fingers. If you conceptualize your fingers as water balloons around bones, you can understand how the internal pressure of your fingers rise the harder you press something. This type of information coupled with the "Sensory Homunculus" make for some incredibly fulfilling thought experiments.
The temperature question is something I'm particularly interested in. Using a colder fluid to model a room temperature fluid because of the heat transfer equation is a fascinating area of scientific problem solving. If you think it through, everything about this boils down to differential equations. How much heat is leaking out of the hand, and at what rate, through what contact area?
