  With a semiclassical quasistatic model we identify the distinct roles of
nuclear Coulomb attraction, final state electron repulsion and electron-field
interaction in forming the finger-like (or V-shaped) pattern in the correlated
electron momentum distribution for Helium double ionization [Phys. Rev. Lett.
\textbf{99}, 263002; \emph{ibid}, 263003 (2007)]. The underlying microscopic
trajectory configurations responsible for asymmetric electron energy sharing
after electron-electron collision have been uncovered and corresponding
sub-cycle dynamics are analyzed. The correlation pattern is found to be
sensitive to the transverse momentum of correlated electrons.
