I don’t get it.

Apparently neither does Box Office Mojo. Even after “Neighbors” earned $2.56 million during Thursday midnight showings—meaning it might do near $50 million over the weekend—BOM’s updated forecast still predicted something closer to $35 million.

Instead, weekend estimates have it at $51 million.

The hell?

Is it Seth Rogen? Doubtful. His best non-animated opening was “The Green Hornet” in January 2011: $33 million. His best live-action comedy opening was “Knocked Up” in 2007: $30 million. He’s not hugely popular and he’s got a laugh like a slushee.

Is it Zac Efron? Doubtful. His previous best non-animated opener was “High School Musical 3: Senior Year,” which grossed $42 million in 2008. His most recent movie, “That Awkward Moment,” opened in January against no competition whatsoever, and grossed just $8.7 million.

Is it the concept? The combination of John Belushi comedies? Instead of the obnoxious guy moving next door it’s the obnoxious frat.

Is it the abs? In the ads?

Is it the love of all things fraternity?

Whatever it is, it’s the 11th-best R-rated opener ever, and the third-biggest R-rated comedy opener ever—after “The Hangover Part II” and “Ted.”

American moviegoers, you fffffascinate me.

Elsehwere, “The Amazing Spider-Man 2” fell of 59% to gross $37 million for second place. In 10 days, it’s now made less ($147 million) than “Spider-Man 3” did in three days ($151). But it’s killing overseas: $403 million in foreign rentals.  

“The Other Woman” hangs in there ($9.2 million for $61 total), as does “Heaven is for Real” ($7 million, $75 total). “Captain America: The Winter Soldier” earned another $5.6 million for $244 million. It’s about $10 million away from eclipsing “The LEGO Movie” as the year’s biggest movie. Until summer movies come along. Or late spring movies.

Good news of a less-perplexing nature? “The Grand Budapest Hotel” made another $1.4 million (11th place), and is now the highest-grossing Wes Anderson movie.

The weekend numbers here.