Young children seem to operate under the assumption that objects always fall in a straight vertical line. When asked to search for a ball dropped down an S-shaped opaque tube, they repeatedly search directly below. Hood proposed that children have difficulty in inhibiting their prepotent expectation that objects fall in a straight line (Hood, 1995). We asked whether the inability to inhibit this prepotent response is the only factor determining children's performance on the tubes task. In one condition the openings to the tubes were covered by chimneys, whereas in another condition the openings were visible. When first tested with the apparatus, children performed better when the openings were visible. Furthermore, children's performance on equally complex configurations (i.e., with or without chimneys) was modulated by their previous experience. Thus, children's understanding of the tubes mechanism seems to play an important role in addition to inhibitory control.