Zoom of a small part of the preceding Fig. 3, bottom of the last frame, showing at the bottom the scale of apparent velocities measured using the FLCT algorithm at ultimate resolution. Pixel size is 0.1 arcsec and time cadence only 1.6 s. An artifact is produced outside the structures with arrows pointing upward. The method is not suitable for measuring proper motion when the velocity is aligned along an extended fine structure as in the case of a vertical, up or down, flow along a quasi-radial spicule.