  It is argued that the observation of anisotropic azimuthal distribution of
final state particles alone is insufficient to show whether the formed matter
at RHIC behaves like hydrodynamic flow. Examining the intrinsic interaction (or
correlation) of the formed matter should provide more definite judgement. To
the end, a spatial-dependent azimuthal multiplicity-correlation pattern is
suggested. It shows clearly in the pattern that there are two kinds of
interactions at the early stage of Au + Au collisions at $\sqnn=200$ GeV
generated by RQMD with hadron re-scattering and AMPT with string melting. This
is out of the expectation from the elliptic flow driven by anisotropic
expansion.
