Rhodopsin is a light-activated G protein-coupled receptor that induces the signaling cascade leading to vision. Isomerization of the 11-cis chromophore to all-trans triggers the visual transduction process. Borhan et al. have trapped the photoisomerization intermediates and have traced changes in the interaction between the chromophore and the protein by photoaffinity labeling. They show that the isomerization occurs with minimal movement of the chromophore ring, leading to a highly strained intermediate. This energy is used to flip the ring, which is accompanied by conformational changes in the protein.