  We analyze interrelation of quantum and classical entanglement. The latter
notion is widely used in classical optic simulation of some quantum-like
features of light. We criticize the common interpretation that "quantum
nonlocality" is the basic factor differing quantum and classical realizations
of entanglement. Instead, we point to the breakthrough Grangier et al.
experiment on coincidence detection which was done in 1986 and played the
crucial role in rejection of (semi-)classical field models in favor of quantum
mechanics. Classical entanglement sources produce light beams with the
coefficient of second order coherence $g^{(2)}(0) \geq 1.$ This feature of
classical entanglement is obscured by using intensities of signals in different
channels, instead of counting clicks of photo-detectors. Interplay between
intensity and clicks counting is not just a technicality. We elevate this issue
to the high foundational level.
