Thor

Anthony Hopkins played the part of Odin, aka the father of Loki (Tom Hiddleston) and Thor (Chris Hemsworth). When he's yelling at Thor, Loki steps in to uncharacteristically defend his brother.  Odin then growls at his son, which Hiddleston didn't expect. The reaction on his face is a genuine surprise reaction. The actors had trouble finishing the scene without laughing!