A key moment called for Henstridge to knock De Caestecker unconscious with a fire extinguisher, an act she rehearsed repeatedly…Despite the practice and the extinguisher’s soft, rubber material, Henstridge was convinced she would hurt De Caestecker. Throughout the day she practiced bumping people on the back of the head…to make certain she could sell the gag without hurting her victim. When it came time to shoot, Henstridge still was hesitant to hit De Caestecker with the necessary force. After much coaxing, she took a good swing and sent him crumpling to the ground in pain. It was a brilliant moment of acting. Ever the prankster, De Caestecker enlisted the help of the on-set makeup team to creative a massive bruise on the back of his neck and feigned injury for most of the next day. A distraught Henstridge fell for the ruse completely.
Agents Of SHIELD Season One Declassified book