Tim Brennen in Psyche:
Indeed, the study of lying is at least a century old, and thousands of scientific papers have been published. Researchers have mainly focused on the two key questions raised by that quote from Freud and the anecdote from India, namely: how good is the average person at detecting lies; and what, if any, are the behavioural signs of lying?
To answer the first question, researchers have typically shown participants video clips of people telling a story. In some studies, the videos are from real life, in other studies they are artificial, but in all cases the researcher knows which ones show someone telling the truth and which show someone lying, and the job of the research participants is to decide for each clip whether the person is lying or not.