Mathematics - Nic Svenson and Piers Barnes of the Australian Commonwealth Scientific and Industrial Research Organization, for calculating how many photographs a person must take to almost ensure that no one in a group photograph will have their eyes closed: "Blink-Free Photos, Guaranteed."

"He found that photographing thirty people in bad light would need about thirty shots. Once there's around fifty people, even in good light, you can kiss your hopes of an unspoilt photo goodbye."

"Piers also came up with a rule of thumb for calculating the number of photos to take for groups of less than 20: divide the number of people by three if there's good light and two if the light's bad."

So now you know.