Zac Efron's Tumble Off Tricycle Had Hugh Jackman Cracking Up!!!

Hugh Jackman laughed his ass off -- and wanted everyone to join in -- when he witnessed Zac Efron falling off a tricycle and tasting asphalt.

Hugh and Zac threw on their circus garb Friday in Midtown Manhattan to film a circus musical for James Corden's late night show. They were promoting "The Greatest Showman" and their co-star Zendaya got in on the action too ... and also busted an LOL at Zac.

We're guessing Zac's caption on this photo gallery would be ... The crap I gotta do to sell a movie.