Poor, poor (poor x10) Mark Ruffalo, he tries hard to do the press tours and also to just drop a video here and there on social media, and then, BOOM! Massive spoiler somewhere! Granted this doesn't happen every time, but it happens enough where he kinda-sorta gets in trouble, at least that's what he hinted at last summer when he let something slip in his excitement to talk of the upcoming ensemble movie that saw the heroes together on screen.
Don Cheadle tries but it's too late... Ruffalo had already said it: "Wait until you see this next one.... Everybody dies. Well, half." Cheadle tries to cut him off after the fact to which Ruffalo amends it with, "Oh, not everybody. Not- err- Can we rewind that part?"
He later looks so embarrassed that he could've possible spoiled once more, even asking Cheadle if he thinks he's in trouble again, and Cheadle tries to assure him he'll be fine towards the end when Ruffalo looks a bit distraught he could have done it again. (Aww!)
Ruffalo's known for spoiling, and every time, it's an accident. The same for his young co-star Tom Holland, who gets super excited and lets things slip. Though... it seems there's a little mystical intervention on occasion.
I think that's what our resident gamma-radiated scientist needs, a little mystical help in keeping the secrets- well, secret. Just pair Doctor Strange with these two and nothing will get out!