Mode bifurcation was investigated when water was poured into a cup. Three modes, i.e., accumulation flow (mode I), scattering flow (mode II), and oscillatory flow (mode III), were regulated by the flow rate and the size of the tube through which the water was poured. When the tube was wide, the flow rate at bifurcation from mode I to mode II was different from that from mode II to mode I, i.e., hysteresis was observed. Mode III was observed only when the flow rate was increasing and the tube was narrow. The water hollow was an important factor in mode bifurcation. The behavior of the system was reproduced by a numerical simulation using differential equations that included the dynamics of two variables, the radius of the water hollow and the pressure exerted on the water hollow. (C) 2003 American Institute of Physics.