Optical spectroscopy of the blue star KIC 10449976 shows that it is an extremely helium-rich subdwarf with effective temperature T _ { eff } = 40 000 \pm 300 K and surface gravity \log g = 5.3 \pm 0.1 . Radial-velocity measurements over a five-day timescale show an upper variability limit of \approx 50 \pm 20 km s ^ { -1 } . Kepler photometry of KIC 10449976 in both long and short cadence modes shows evidence for a periodic modulation on a timescale of \approx 3.9 days . We have examined the possibility that this modulation is not astrophysical but conclude it is most likely real . We discuss whether the modulation could be caused by a low-mass companion , by stellar pulsations , or by spots . The identification of any one of these as cause has important consequences for understanding the origin of helium-rich subdwarfs .