Birdman did not win any of its three acting prizes—even though it's obvious that the actors loved it. The film won the Screen Actors Guild award for Best Ensemble, and also won the Best Picture Oscar (actors make up the highest percentage of the voting body by far).
It would've been fitting if star Michael Keaton won because Birdman is a movie built around him, and the superhero worlds that he was once a part of. And Oscar loves a career award. But Oscar also loves actors acting out a physical affliction, and Eddie Redmayne—who played Stephen Hawking, the brilliant physicist who suffered from ALS—had a physically transforming performance going for him.
Redmayne has only acted in 15 films. So when he won, his body had a lot of different reactions:
Keaton started acting back in 1977. It appears that he had a speech prepared for if he had won (but that's probably only to make the best use of his time if he were to win—which was certainly a possibility. Keaton probably didn't want to skwee and worship his Oscar like Redmayne ended up doing).
Heartbreakingly, he had to stuff it back into his jacket. Keaton was in the front row, so it briefly showed on the broadcast.
When Birdman did win Best Picture, however, director Alejandro González Iñárritu did ask Keaton to speak. And Keaton said, off the cuff, not from a card, "This has been a tremendous experience." He continued, "These guys are as bold as bold could be, it was just a tremendous honor for me – look, it's great to be here who am I kidding, this is just great fun, thank you very much."
With Birdman providing a career shot in the arm, Keaton has three roles upcoming: Spotlight (as an editor at The Boston Globe when they discovered a Catholic church pedophile cover-up), The Founder (playing Ray Kroc, the man who franchised McDonald's, taking the burger stand away from the McDonalds), and Kong: Skull Island. Maybe he'll be back at the Oscars.
Regardless, he'll always be Batman. And Birdman.