When cats purr they emit alpha waves which have a calming effect on us. Drinking tea has a similar effect. In addition to the stimulating theine, tea contains the amino acid L-theanine which triggers those alpha waves in the brain. These, in turn, are responsible for the reward hormone dopamine which relaxes us. This makes tea, for two reasons, the most enjoyable way to optimise our own performance - it is the perfect combination of stress buster and euphoria inducer.