  Mid-late M stars are opportunistic targets for the study of low-mass
exoplanets in transit because of the high planet-to-star radius ratios of their
planets. Recent studies of such stars have shown that, like their early-M
counterparts, they often host multi-resonant networks of small planets. Here,
we reanalyze radial velocity measurements of YZ Ceti, an active M4 dwarf for
which the HARPS exoplanet survey recently discovered three exoplanets on
short-period (P = 4.66, 3.06, 1.97 days) orbits. Our analysis finds that the
orbital periods of the inner two planets cannot be uniquely determined using
the published HARPS velocities. In particular, it appears likely that the
3.06-day period of YZ Ceti c is an alias, and that its true period is 0.75
days. If so, the revised minimum mass of this planet is less than 0.6 Earth
masses, and its geometric transit probability increases to 10%. We encourage
additional observations to determine the true periods of YZ Ceti b and c, and
suggest a search for transits at the 0.75-day period in TESS lightcurves.
