Making movies usually involves numerous setbacks and modifications, which can also affect the cast. For various reasons, it is very common for a performer to be replaced by another before, during, or even after filming. These modifications can have a significant impact on the final product.

00:00 Introduction
00:21 Viggo Mortensen and Stuart Townsend (The Lord of the Rings)
01:29 Ryan Gosling and Mark Wahlberg (The Lovely Bones)
02:30 Samantha Morton and Scarlett Johansson (Her)
03:33 Jon Finch, John Hurt, and Michael Biehn (Alien and Aliens)
04:40 Harvey Keitel and Martin Sheen (Apocalypse Now)
05:45 Jason Robards/Mick Jagger and Klaus Kinski (Fitzcarraldo)
06:35 Nicole Kidman/Hayden Panettiere and Jodie Foster/Kristen Stewart (Panic Room)
07:40 Kevin Spacey and Christopher Plummer (All the Money in the World)
08:48 Dougray Scott and Hugh Jackman (XMen)
10:15 Eric Stoltz and Michael J. Fox (Back to the Future)