"Hardlight hologram," Bruce supplies, one corner of his mouth tipping upwards. "Stark uses them mostly for his displays, but we've ... kind of been working on something bigger with them."

They both have their own, separate projects, but both of them are also used to multitasking. They're working on making a sort of training room using hardlight holograms, where he and Thor can get into pissing contests without destroying a forest somewhere. Or where he can let the Hulk out without worrying about racking up a hefty repair bill for the city of New York.

If Stark borrowed the idea from some friends up in Westchester, Bruce isn't going to call him on it.