  Vacuum models of charged or spinning black holes possess two horizons, the
inner of which has the oft-overlooked property that gravitational tidal forces
initially spaghettifying a freely falling observer will eventually change signs
and flatten the observer like a pancake. Inner horizons also induce a classical
blueshift instability known as mass inflation, and a number of recent studies
have found that inner horizons exhibit even stronger quantum singular behavior.
In this essay we explore the quantum effect of Hawking radiation, which in the
presence of compressive tidal forces seems to predict negative temperatures. By
analyzing the interaction of quantum fields with black hole geometries, we can
come to a closer semiclassical understanding of what really happens near a
black hole's inner horizon.

General Relativity and Quantum Cosmology