We produce a detailed proof of a result stated in "F. Obersnel and P. Omari, Period two implies chaos for a class of ODEs, Proc. Amer. Math. Soc, 135 (2007), 2055-2058" concerning scalar time-periodic first order differential inclusions. Such a result shows that the existence of just one subharmonic implies the
existence of large sets of subharmonics of all given orders.
