  Let $f$ be a Laurent polynomial in two variables, whose Newton polygon
strictly contains the origin and whose vertices are primitive lattice points,
and let $L_f$ be the minimal-order differential operator that annihilates the
period integral of $f$. We prove several results about $f$ and $L_f$ in terms
of the Newton polygon of $f$ and the combinatorial operation of *mutation*, in
particular we give an in principle complete description of the monodromy of
$L_f$ around the origin. Special attention is given to the class of *maximally
mutable* Laurent polynomials, which has applications to the conjectured
classification of Fano manifolds via mirror symmetry.
