The mechanistic approach is utilized extensively by Paul, Harding and Mendl. Recognizing the difficulty in studying emotion in non-verbal animals, Paul et al. demonstrate possible ways to better examine this. Observing the mechanisms that function in human emotion expression, Paul et al. suggest that concentration on similar mechanisms in animals can provide clear insights into the animal experience. They noted that in humans, cognitive biases vary according to emotional state and suggested this as a possible starting point to examine animal emotion. They propose that researchers may be able to use controlled stimuli which have a particular meaning to trained animals to induce particular emotions in these animals and assess which types of basic emotions animals can experience.