Science sleuths Hannah Fry and Adam Rutherford investigate the following question sent in by Philip Le Riche:

'Why do some people faint at the sight of blood, or a hypodermic needle, or even if they bash their funny bone? Does it serve any useful evolutionary purpose, or is just some kind of cerebral error condition?'

Adam is strapped onto a hospital tilt table in an attempt to make him blackout and Hannah receives an aromatic surprise.

Featuring consultant cardiologists Dr Nicholas Gall and Dr Adam Fitzpatrick and cardiac physiologist Shelley Dougherty.

If you have any scientific cases for the team to investigate please email: curiouscases@bbc.co.uk

Presenters: Hannah Fry & Adam Rutherford
Producer: Michelle Martin.