wick's theorem question

The interaction hamiltonian is say \psi.gamma^mu.\psi.A (for fermion
boson interaction...say coulomb interaction).

Let me take the second order term of the perturbation expansion, and
apply the wicks theorem to get the
nomal ordering.

Let x and y be the two vertex in this second order interaction.

I need to move \psi(x) across the a gamma matrix (in vertex y) before
I can contract it with the initial state
vector |p_i>. The way I read the result in the books, it seems to just
move across as if the gamma matrix is a scalar. I'm a bit confused
here.

Anyone can clarify?

.