  In this paper, we prove that the Extended Courant Property fails to be true
for certain smooth, strictly convex domains with Neumann boundary condition:
there exists a linear combination of a second and a first Neumann
eigenfunctions, with three nodal domains. For the proof, we revisit a
deformation argument of Jerison and Nadirashvili (J. Amer. Math. Soc. 2000,
vol. 13). This argument being interesting in itself, we give full details. In
particular, we carefully control the dependence of the constants on the
geometry of our Lipschitz domains along the deformations.
