Tis the season. Paranormal Activity 3, the latest in the series of films that purport to be "found footage" of creepy events, took in $54 million over the weekend, the biggest October debut in history and the best opening in more than two months. The low-budget prequel's big take far surpassed expectations, with doubters assuming that audiences would have lost interest in the premise — that home-video cameras set up by amateur paranormal-activity investigators recorded the footage — by the third installment. Now, it seems a series that once appeared to be a "one-off, out-of-nowhere discovery two years ago" when the first Paranormal Activity came out has developed into the sort of "long-running, durable franchise that serves as the holy grail for any movie studio." How? Here, three theories:

1. It's a decent movie
"The film is a good scare without using gore as a fallback," Paramount Vice-Chairman Rob Moore tells The Wall Street Journal. Solid reviews (74 percent positive on Rotten Tomatoes) helped to attract older viewers. Nearly half of the weekend's audience, somewhat unexpectedly, was over 25.

2. It's part of a strong brand
"This brand is as solid as the Twilight brand or the Jackass brand. There are certain brands that just transcend any kind of box-office rhyme or reason. They just resonate," says the president of Hollywood.com's box-office division, Paul Dergarabedian, as quoted by the Associated Press. "These are shot in someone's house, they look like they're shot with a home video recorder, and people just relate to it."

3. It's the new Saw
"The distribution team has taken a page out of the book that made Lionsgate's Saw franchise such a safe bet in terms of budgets and profitability," says Jarrod Sarafin at Mania. The first Paranormal Activity was shot for $15,000, and the latest cost only $5 million, making it hugely profitable, just like the low-budget Saw movies. Saw is the "gold standard," says Steven Zeitchik in the Los Angeles Times. A new Saw flick came out every Halloween for seven straight years, starting in 2004, and all but one grossed between $45 and 90 million. "Paranormal would seem well-positioned to carry on the Saw mantle: It has the brand name, the fan base and, now that Saw has wound down its run, the Halloween period to itself." Its "found footage format" conceit might not have the same longevity, however; the films are more rooted in actual storytelling rather than cheap, horror-porn cathartic thrills. "Paramount must walk a tricky line — recycle the same stories and it will turn filmgoers off, but veer in too many new directions and people will wonder what happened to the Paranormal they know and love."