Hot Pack Therapy
Since the last video was about an ice cube this one is about a hot pack.
The pack is one of those re-usable type that is filled with a super-saturated solution of sodium acetate. When you squeeze the little metal tab inside, the acetate nucleates and starts to crystallize, which creates heat.
You can see the growth of crystals inside the pack as a spreading wave of glowing white.
I then use the now hot pack to heat of sections of my face.
It's all terribly scientific.