 Unique smooth flex of a cuspidal cubic

For $D=\{y^{2}z=x^3\}$, the determinant of the homogeneous Hessian matrix is $24x{y}^2$. Its intersections with $D$ are the cusp $[0:0:1]$ and the smooth point $[0:1:0]$. The Hessian criterion for a flex therefore gives a unique smooth flex, with tangent $z=0$ and contact order three. Consequently every pair consisting of a triple line and a cuspidal cubic meeting only at a smooth point is projectively equivalent to $(3\{z=0\},D)$.