What Is The Repetition Technique?

Sanford Meisner, one of the few real method acting gurus of the Twentieth Century.  He developed a technique called the Repetition Exercise, Game or Technique (depending upon who you ask).

This technique is developed to force the actor into behaving truthfully on stage.  Meisner was fond of saying, that acting was living truthfully under the imaginary circumstances of the play.
This exercise is developed to get the actors to live truthfully and respond truthfully to one another.

The game is simple. Both actors stand facing each other (sometimes they sit) and one notices something about the other and states it clearly.  

'You have a blue tie'

The partner then repeats from their perspective -

'I have a blue tie'

They then repeat (that's where the name comes from!)

Back and forth they go until something happens, they either burst into laughter or something chances of its own volition.  

Being able to do this exercise well is extremely difficult, behaving naturally is very difficult, especially for actors who have been trained to 'pretend'.