  The dominant phonon wavevectors $q^{*}$ probed by the 2D Raman mode of
graphene are highly anisotropic and rotate with the orientation of the
polarizer:analyzer direction relative to the lattice. The corresponding
electronic transitions connect the electronic equibandgap contours where the
product of the ingoing and outgoing optical matrix elements is strongest,
showing a finite component along $\bm{K}-\bm{\Gamma}$ that sensitively
determines $q^{*}$. We revoke the notion of 'inner' and 'outer' processes. Our
findings explain the splitting of the 2D mode of graphene under uniaxial
tensile strain. The splitting originates from a strain-induced distortion of
the phonon dispersion; changes in the electronic band structure and resonance
conditions are negligeable for the 2D Raman spectrum.
