  I discuss some simple aspects of the low-energy physics of a nontrivial scale
invariant sector of an effective field theory -- physics that cannot be
described in terms of particles. I argue that it is important to take seriously
the possibility that the unparticle stuff described by such a theory might
actually exist in our world. I suggest a scenario in which some details of the
production of unparticle stuff can be calculated. I find that in the
appropriate low energy limit, unparticle stuff with scale dimension
$d_{\mathcal{U}}$ looks like a non-integral number $d_{\mathcal{U}}$ of
invisible particles. Thus dramatic evidence for a nontrivial scale invariant
sector could show up experimentally in missing energy distributions.
