Hereditary premiered in the number four box office spot this weekend, preceded by guerrilla marketing campaigns that helped lure an estimated audience of 1.4 million.

A24’s art-house horror flick marked a new high for the distributor, beating industry expectations and bringing in an estimated $13 million dollars within its first weekend.

The success of Hereditary’s opening weekend may boil down to its marketing, which garnered curiosity and conversation on social media. Attendees of a midnight screening found dolls on their doorsteps the next morning, for example, and other viewers were asked to wear a heart monitor.

“I think the dolls are a great idea,” Karie Bible, box office analyst and film historian at Exhibitor Relations, told AListDaily. “It is creepy and will easily go viral. Basically, the gist is to give the public a creepy PR stunt and they will spread the word via social media.”

Hereditary is far from the being the first to employ such marketing around a horror film, with PR stunts going back to the early days of film.

“Lon Chaney’s look as the ‘Phantom’ was kept out of all promotional material surrounding the 1925 release of Phantom of the Opera,” recalled Bible. “They wanted his terrifying makeup to be a surprise when it was finally unveiled.”

Reports indicate that nurses and ambulances were parked outside of movie theaters playing Frankenstein in 1931, standing by to help people who had fainted due to fright. Director/producer William Castle (Rosemary’s Baby, 13 Ghosts) took this technique well into the 1950s and ’60s, Bible added, awarding “coward certificates” to those who left the theater early or offering a life insurance policy for those who feared dying of fright.

“I think horror films can succeed at any time if they manage to strike a chord with audiences,” said Bible. “In the summer of 2017 Annabelle: Creation grossed $102 million. The summer of 2016 saw The Conjuring 2 rake in $102 million. The conventional wisdom is to release horror films on or around Halloween [but] that can often create a crowded marketplace and split the audience. Sometimes unconventional release dates can work to a film’s advantage.”