  The property of the ``perfect liquid'' created at RHIC is probed with
anisotropic flow measurements. Different initial conditions and their
consequences on flow measurements are discussed. The collectivity is shown to
be achieved fast and early. The thermalization is investigated with the ratio
of $v_4/v_2^2$. Measurements from three sectors of soft physics (HBT, flow and
strangeness) are shown to have a simple, linear, length scaling. Directed flow
is found to be independent of system size.
