'Thor: Ragnarok' star accidentally livestreams part of movie

In a Hulk-sized goof, Mark Ruffalo apparently stuffed his phone in his pocket, and went into a screening with Instagram merrily streaming away.

Some Instagrammers were treated to an audio-only sneak peek at "Thor: Ragnarok," courtesy of star Mark Ruffalo.

Fans who've been counting the days until the Nov. 2 premiere of "Thor: Ragnarok" were gifted a little sneak peek on Tuesday night. Star Mark Ruffalo was livestreaming to Instagram from the red carpet of the Los Angeles premiere. But once the film began to roll, he seems to have pocketed his phone without turning the streaming function off.

Ruffalo accidentally (we think) streamed about 15 minutes of the Marvel superhero film, in which he plays the Incredible Hulk. The stream had no video, just audio of the film, complete with audience laughs and cheers. According to The Hollywood Reporter, about 2,500 people were watching the stream at one point.

The stream was quickly shared around the web, but we're not going to link to those shares -- it's a weird way to spoil the beginning of a film anyway.

Earlier that day, while driving to the theater, Ruffalo announced in a video on Instagram, "We're going to take over Instagram for the amazing premiere of 'Thor: Ragnarok.'" But he had no idea the takeover would involve such a Hulk-sized goof. Of course, there's always the chance this was a PR stunt, but if so, it was an odd one.

Here's a still image of what viewers saw:

This wasn't Ruffalo's first Marvel-ous mistake. Back in July, he told "Good Morning, America" about some supposed bad news facing the Avengers in "Infinity War." (But we're not buying that as an actual spoiler, for numerous reasons.)

Twitter reactions were worth the (free) price of admission.