A three-year-old boy has revealed his surprisingly comprehensive knowledge of the human immune system during an accidental encounter with a medical student.

In a post to the Love What Matters Facebook page , US-based medical student P. Salehi said she was visiting a grocery store when “Anson” struck up a conversation with them.

“Since I was wearing my Morehouse School of Medicine shirt, he asked me what type of doctor I'm going to be and eventually expressed his passion for the immune system to me,” Ms Salehi wrote.

Video recorded by Ms Salehi of the conversation, which lasted more than 10 minutes, shows the boy waiting in the infant seat of a shopping trolley, casually discussing the finer points of brain anatomy, the nervous and immune systems.

The video has since received hundreds of thousands of views as well as thousands of reactions and shares.

Facebook users have marvelled at Anson’s remarkable powers of recall.

“‘Calling Harvard medical school’. ‘Yes, hello?’ ‘You have a new applicant’,” user Ilina Kay wrote.