Actor Tyler Posey and his Truth or Dare castmates had no idea the casual vacation footage they filmed on their phones would end up as the opening sequence of the new horror film.

Tyler and his co-stars were flown to Mexico ahead of production on the scary movie at the behest of director Jeff Wadlow, who wanted the cast to develop real-life bonds to enhance the friendships onscreen.

As soon as the actors arrived on the sandy beaches of Rosarito, they started gleefully filming their escapades on smartphones, only to discover later that the random footage would actually end up in the movie.

"We did not know that we were going to film the opening title sequence," Tyler recalls to Collider. "(Director) Jeff wanted us to go to Mexico, as a cast bonding trip, to get to know one another, so that the friendships felt really real.

"I think it was just an added bonus to possibly film our opening title sequence on our phones, to make it seem like we actually lived out that week in Rosarito, but it turned out to be really, really, really good, and we got great footage."

Posey stars alongside Lucy Hale in the new film, about a group of college seniors who vacation in Mexico together for the last time before graduating university, only for a silly game of truth or dare to turn spooky and deadly.

Calling his castmates "super talented and super passionate" people, Tyler absolutely loved filming the movie, but the former Teen Wolf admits there was one gory element he thought Truth or Dare needed more of.

"I wish there was more blood, honestly," he laughs. "I had a great time on Teen Wolf, with all of the blood on that show. There was not enough blood for me (on this). There’s definitely a lot of blood in the movie, but I wasn’t covered in it enough."

However, he thinks fans will be shivering in their seats when they see the horror film.

"I think scary movies are way scarier when there’s less to see, if that makes any sense," he winks.

Truth or Dare hits U.S. theatres on Friday (13Apr18).

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