In 2016, Hamill responded to a fan who asked if that was indeed his head in the “Empire Strikes Back” dream sequence. He noted that it was, saying simply that, “It was my head protruding through an opening in the set floor as I stood below — My prop head was tested but rejected.”
“Star Wars” obsessives naturally had some of the test photos of the Mark Hamill prop head, and an image of it eventually surfaced in Hamill’s Twitter feed the following year. One can take a look at it and judge for themselves if the filmmakers made the right choice. It’s a high-quality rubber head, of course, but it doesn’t look exactly like Hamill. The actor’s comment: “Unused dummy head — rejected in favor of using my real head pushed up from beneath the set. Hard to keep my eyes open [with] all that smoke!”
Since Yoda was a puppet operated by Oz, the Dagobah set was already elevated, making the real-head effect that much easier to achieve.
Hamill, when playing his own severed head, had to keep his dead eyes wide open as the smoke cleared from the mask blowing open. No, his head wasn’t inside the mask when it exploded, but the smoke lingered on the set. Hamill doesn’t mention how many takes it took for the shot to look right, but one can imagine it wasn’t too many.
Released last year, the docuseries “Light and Magic” contained a scene in which some of the men who worked for Industrial Light and Magic (the special visual effects, animation, and virtual production division of Lucasfilm) looked through an old prop warehouse in 1988, and they found the rubber head. They joked that it looked terrible and treated the prop rather indelicately.
The head’s current location is unknown, although it’s likely in the same ILM archive as it was in 1988.