  "Perytons" are millisecond-duration transients of terrestrial origin, whose
frequency-swept emission mimics the dispersion of an astrophysical pulse that
has propagated through tenuous cold plasma. In fact, their similarity to FRB
010724 had previously cast a shadow over the interpretation of "fast radio
bursts," which otherwise appear to be of extragalactic origin. Until now, the
physical origin of the dispersion-mimicking perytons had remained a mystery. We
have identified strong out-of-band emission at 2.3--2.5 GHz associated with
several peryton events. Subsequent tests revealed that a peryton can be
generated at 1.4 GHz when a microwave oven door is opened prematurely and the
telescope is at an appropriate relative angle. Radio emission escaping from
microwave ovens during the magnetron shut-down phase neatly explain all of the
observed properties of the peryton signals. Now that the peryton source has
been identified, we furthermore demonstrate that the microwaves on site could
not have caused FRB 010724. This and other distinct observational differences
show that FRBs are excellent candidates for genuine extragalactic transients.
