Snapping

The Tenth Doctor snaps his fingers. (TV: Forest of the Dead)

Snapping was an act which could be performed by one's fingers.

Initially, the Tenth Doctor believed that one could not open the doors of the TARDIS by snapping one's fingers. However, he learnt from River Song that he would do so in his future. Indeed, following their encounter, the Doctor successfully opened the doors with a snap of his fingers. (TV: Forest of the Dead) The finger snapping method of opening the TARDIS doors would not be used often until the Doctor's eleventh incarnation. (TV: The Eleventh Hour, Day of the Moon, The Doctor's Wife)

Clara Oswald was also capable of opening the TARDIS doors by snapping her fingers, having done so on two occasions. (TV: The Day of the Doctor, The Caretaker)

In the year 200,000, those aboard Satellite Five who had the infospike implant could activate it by a snap of the fingers. This was the default method of activation, but could be changed by the individual who had the procedure. (TV: The Long Game)

Snapping one's fingers was also a means of getting an individual's attention. Mickey Smith snapped his fingers at Melissa, a Deffry Vale High School pupil, in an attempt to break her out of a trance induced by the Krillitanes. (TV: School Reunion) The Tenth Doctor likewise attempted this with Adeola Oshodi after her conversion into a Cyber-agent. (TV: Army of Ghosts)