We show that there is a bar-and-joint framework G(p) which has a confi
guration p in the plane such that the component of p in the space of a
ll planar configurations of G has a cusp at p. At the cusp point, the
mechanism G(p) turns out to be third-order rigid in the sense that eve
ry third-order flex must have a trivial first-order component. The exi
stence of a third-order rigid framework that is not rigid calls into q
uestion the whole notion of higher-order rigidity.