10 Horror Movies That Made It Up As They Went Along (But Were Awesome Anyway)

28 Days Later is among the most influential horror films of the last 20 years, since it's directly responsible for popularising the "running zombies" subgenre.

But another factor that made Danny Boyle's movie stand out is the air-tight script. The dialogue is so well-written, it feels like not a single line was wasted. This is even more impressive when you learn the second-half was made up in the eleventh hour.

At the halfway point, Frank becomes infected with Rage, compelling him to attack his group. In the original script, Jim knocked him out, allowing the group to transport Frank to a hospital.

While there, Jim encountered a scientist who informs the group they can return Frank to normal by giving him a full-body transfusion. Jim uses his blood to cure Frank, but is turned into a Rage-infected monster himself.

But because a single drop of Rage blood will infect anyone, Boyle realised the procedure was impossible unless you "clean out every capillary and vein with bleach before making the transfusion". Realising that the story had hit a wall, Boyle had to redo the entire third act.