We have recently been investigating the magnitudes and signs of the interaction terms in the potential functions of triatomic molecules XYZ. These arise from interactions between two bond-lengths (XY and YZ), or between one bond-length and the angle XYZ. In our study of these terms we have distinguished three distinct effects: (1) resonance effects; (2) interaction between nori-bonded atoms (here X and Z); (3) changes of hybridization at the central atom (here Y). A proper understanding of all three of these is necessary before even the signs of the interaction terms can be adequately explained.