The authors discuss the physical nature of electron sound signals excited in molybdenum by an acoustic wave and propagating at the Fermi velocity. The experimental temperature dependences of the amplitude and the phase velocity of these signals have been studied in the normal and superconducting state. They interpret this effect observed earlier in Ga by Burma et al. as the excitation of a weakly damped zero-sound wave caused by the Fermi-liquid interaction between charge carriers. A dominating role of the electron-electron collisions in the zero-sound damping in Mo was established, and the corresponding relaxation time was estimated. Theoretical calculations of the expected zero-sound behaviour in a superconductor are in good agreement with the experimental data and enable them to determine the intensity of the Fermi-liquid interaction.