  All species of (non-conformally-coupled) particles are produced during
inflation so long as their mass $M$ is not too much larger than $H$, the
expansion rate during inflation. It has been shown that if a particle species
that is normally massive ($M\gg H$) couples to the inflaton field in such a way
that its mass vanishes, or at least becomes small ($M < H$), for a particular
value of the inflaton field, then not only are such particles produced, but an
irruption of that particle species can occur during inflation. In this paper we
analyze creation of a massive particle species during inflation in a variety of
settings, paying particular attention to models which realize such an irruptive
production mechanism.
