  The first year of observations by the Planck satellite mission shows that the
cosmic microwave background (CMB) fluctuations are consistent with gaussian
statistics in the primordial perturbations, a key prediction of the simplest
models of inflation. However, there are hints of anomalies in the CMB power
spectrum and bispectrum. We check for the possibility that some of these
anomalous features have a common physical origin in a transient reduction of
the inflaton speed of sound. We do this by exploiting predicted correlations
between the power spectrum and bispectrum. Our results suggest that current
data might already be sensitive enough to detect transient reductions in the
speed of sound as mild as a few percent. Since this is a signature of
interactions, it opens a new window for the detection of extra degrees of
freedom during inflation.
