  KIC 5773205 is the least luminous eclipsing M dwarf found in the Villanova
catalog of eclipsing binaries detected by the {\it Kepler} mission. We
processed and analyzed the three available quarters of mission data for this
star and discovered a persistent periodic variation of the light curve with a
period, which is in exact 4:5 commensurability to the orbital period. Three
routes of interpretation are considered: 1) non-radial pulsations excited by
the tidal interaction at a specific eigenfrequency; 2) a high-order spin-orbit
resonance caused by the tides; 3) an ellipsoidal deformation caused by an outer
orbiting companion in a mean motion resonance. All three explanations meet
considerable difficulties, but the available facts seem to favor the tidally
driven pulsation scenario. The star may represent a new type of heartbeat
binary with tidally excited pulsations that are close to the orbital motion in
frequency.
