Movies are forever. Movie scripts, on the other hand, are hardly set in stone. Throughout the history of cinema, some of the best, most iconic lines that ever existed were created on the spot, delivered accidentally, or made up by the inventive minds of Hollywood actors.

There’s no shortage of iconic improvised lines in this compilation, from Orson Welles’ The Third Man to Walt Disney’s Frozen! And some of these are so good, clever, and memorable that it’s almost unbelievable to think they were never part of plan A. Has your favorite film made it to the list?

“Want to Hear the Most Annoying Sound in the World?” (Dumb and Dumber)

Improvised lines are pretty standard in comedy flicks, especially when you can count on people as talented as the one and only Jim Carrey. A genius comedic figure, Carrey was perfect in the role of the hilarious imbecile Lloyd from Dumb and Dumber.

In the 1994 movie, one of Carrey’s most famous improv lines happened when he asked Harry if he wanted to hear “the most annoying sound in the world.” In true Jim Carrey fashion, Lloyd delivered on his promise and made a poor hitchhiker feel utterly annoyed. In the scene, you can see Carrey briefly go off-character before delivering the unscripted line.