Temporal evolution of dark filaments and umbral dots. The images correspond to the field of view indicated by the dotted white box in Figure 3. The frames have a cadence of 100 s and show a UD traveling from the end of one dark filament F2 to the flank of another filament F1. The black plus and cross symbols denote the initial and final positions of the UD in the time sequence, respectively. Each major tick mark corresponds to 0 5.