Being John Malkovich
Being John Malkovich certainly did a lot of unusual filmmaking things, to say the least. Learning that a huge chunk of it was improvised comes as no surprise. In particular, we would like to direct your attention to the scene when an extra throws a can at the title character right after saying, “Hey Malkovich! Think fast!” That bit was improvised by a drunk extra, apparently.
The Usual Suspects
Can you believe the lineup bit in The Usual Suspects was improvised? You would be even more surprised and entertained if you learned why. Apparently, the actors could not stop laughing after Benicio Del Toro kept releasing gas. When the star was told off by the director, the others had a harder time keeping a straight face. The director simply resigned and embraced the change in tone instead!