MCU: 10 Fascinating Facts Behind Avengers: Age Of Ultron (2015)

6. The Wolf, The Ram And The Hart

During Thor's confusing vision when Scarlet Witch uses her powers on her, he's taken to a grotesque version of Asgard where he briefly sees three men wearing masks that look like a wolf a ram, and a hart (more commonly known as a "stag").

This is a very subtle Easter Egg reference to Whedon's other bog franchise - the Buffy universe and specificlly Angel, where The Wolf, The Ram and The Hart are three ancient demons masquerading as a law firm called Wolfram & Hart who are the chief villains of the show:

“I try not to be self-indulgent. I just had a feeling that there was a connection between the evils of this world and the evils of all worlds. There is that one shot in Thor’s dream that is in an archway with three guys wearing three masks. The masks are very expressionistic. It might be hard to see exactly what they are and we only held on them for a moment. But they were originally seen over a line of Thor’s that was taken out where he says, ‘It’s been a long journey and dark forces followed me.’ …basically, though expressionistic, they are based on three animals. A wolf, a ram and a hart. Some of you might know what that means to me.”