  We dynamically analyze our experimental results on the motion sensitive
spiking H1 neuron of the fly's visual system. We find that the fly uses an
alphabet composed of a few letters to encode the information contained in the
stimulus. The {\em alphabet dynamics} is multifractal both with and without
stimulus, though the multifractality increases with the stimulus entropy. This
is in sharp contrast to models generating independent spike-intervals, whose
dynamics is monofractal.
