  The Feynman propagator encodes all the physics contained in a free field and
transforms as a covariant bi-scalar. Therefore, we should be able to discover
the thermality of the Rindler horizon, just by probing the structure of the
propagator, expressed in the Rindler coordinates. I show that the thermal
nature of the Rindler horizon is indeed contained --- though hidden --- in the
standard, inertial, Feynman propagator. The probability $P(E)$ for a particle
to propagate between two events, with energy $E$, can be related to the
temporal Fourier transform of the propagator. A strikingly simple computation
reveals that: (i) $P(E)$ is equal to $P(-E)$ if the propagation is between two
events in the same Rindler wedge while (ii) they are related by a Boltzmann
factor with temperature $T=g/2\pi$, if the two events are separated by a
horizon. A more detailed computation reveals that the propagator itself can be
expressed as a sum of two terms, governing absorption and emission, weighted
correctly by the factors $(1+n_\nu)$ and $n_\nu$ where $n_\nu$ is a Planck
distribution at the temperature $T=g/2\pi$. In fact, one can discover the
Rindler vacuum and the alternative (Rindler) quantization, just by probing the
structure of the inertial propagator. These results can be extended to local
Rindler horizons around any event in a curved spacetime. The implications are
discussed.
