I saw the movie and it is quite violent.
We have an 8-year old and her dad and mom have been taking her to see PG 13 (and even some R) movies for a long time. At age 4 she saw Chucky! At age 7 she saw The Grudge!
She doesn't have nightmares, these movies don't seem to bother her. In fact, she'll often say "oh, it's just a movie." So it SEEMED like she was okay with seeing PG-13 and R movies.
Well, until recently. You see, these movies were going over her head. WAAAAY over her head. So much in fact that she wasn't even seeing it as a movie, just a bunch of action scenes. And she was so convinced that it wasn't "real" that things in movies that ARE real she refused to believe existed. She would watch the movie, not understand it and say she loved it (because that's what adults expected her to say). And she was carrying that over into school, reading etc. She got VERY GOOD at pretending to understand things. So much so that she fooled all her teachers.
Just recently a lightbulb went off in her head and she's been eager to understand things. She can't even understand SIMPLE MOVIES for kids younger than her. If you ask her specific questions, she has NO IDEA what's going on. But boy can she pretend! And now that she's getting an UNDERSTANDING of movies, she's quite horrified at what she's seeing. Movies that she saw dozens of times she now understands and doesn't like because she now knows what's going on.
What I'm trying to say is that just because your kid doesn't seem scared doesn't mean that you should show them the movies. They have ratings for a reason. The damage isn't always just being scared, but could be the opposite which is a complete lack of understanding, or they could make up their own reasons for things they don't understand. That's just as damaging.