  We consider theoretically density-density correlation of identical Fermi
system by including the finite resolution of a detector and delta-function term
omitted in the ordinary method. We find an anomalous fermion bunching effect,
which is a quantum effect having no classical analogue. This anomalous fermion
bunching is studied for ultracold Fermi gases released from a three-dimensional
optical lattices. It is found that this anomalous fermion bunching is supported
by a recent experiment (T. Rom et al Nature 444, 733 (2006)).
