  This paper discusses the locality and analyticity of the crossing symmetric
dispersion relation (CSDR). Imposing locality constraints on the CSDR gives
rise to a local and fully crossing symmetric expansion of scattering
amplitudes, dubbed as Feynman block expansion. A general formula is provided
for the contact terms that emerge from the expansion. The analyticity domain of
the expansion is also derived analogously to the Lehmann-Martin ellipse. Our
observation of type-II super-string tree amplitude suggests that the Feynman
block expansion has a bigger analyticity domain and better convergence.
