Revealing mistake: Tanner Boatwright was used as a leg double for Augustus. In the part of the sex scene where they shoot from the feet up, you can see that the amputated thigh is thinner and has a slightly different colored tone of leg hair than Ansel's actual leg. (01:05:25)
The Fault in Our Stars (2014)
1 revealing mistake - chronological order
Directed by: Josh Boone
Starring: Laura Dern, Shailene Woodley, Ansel Elgort, Nat Wolff
Continuity mistake: When Hazel shows her hand in support group (when Gus is present) the girl near her has her collar open but as she stands up the girl has her collar closed. (00:09:10)
Hazel: Even though you have freaking cancer, you are willing to give money to corporation for a chance to acquire even more cancer? Let me just assure you that not being able to breathe SUCKS. Totally disappointing. Totally.
Augustus: They don't kill you unless you light them. And I've never lit one. It's a metaphor, see: You put the killing thing right between your teeth, but you don't give it the power to do its killing. A metaphor.
Trivia: Dr. Maria is an actual oncologist who served as the oncologist for most of the members of the support group.