  We first revisit Hartle and Hawking's path integral derivation of Hawking
radiation. In the first point of view, we interpret that a
particle-antiparticle pair is created and the negative energy antiparticle
falls into the black hole. On the other point of view, a particle inside the
horizon, or beyond the Einstein-Rosen bridge, tunnels to outside the horizon,
where this computation requires the analytic continuation of the time. These
two faces of the Hawking radiation process can be extended to not only
particles but also fields. As a concrete example, we study the thin-shell
tunneling process; by introducing the antishell as a negative tension shell, we
can give the consistent interpretation for two pictures, where one is a
tunneling from inside to outside the horizon using instantons, while the other
is a shell-antishell pair-creation. This shows that the Euclidean path integral
indeed carries vast physical implications not only for perturbative, but also
for non-perturbative processes.
