We explore gauge fields-strings duality by means of the loop equations and the zigzag symmetry. The results are striking and incomplete. Striking — because we find that the string ansatz proposed in [? ] satisfies gauge theory Schwinger-Dyson equations precisely at the critical dimension D cr=4 . Incomplete — since we get these results only in the WKB approximation and only for a special class of contours. The ways to go beyond these limitations and in particular the OPE for operators defined on the loop are also discussed.