Jane knew she would be thrown into the water?

Did Jane Birkin know that she would be thrown into the water? I know that she is a great actress but the hostility that she projects after getting out of that indoor pond seems to indicate that she did not know it was part of the script! Does anybody know?? I have heard of directors having an actor doing something to another actor, without warning, in order to get a better and more authentic reaction from the actor receiving the action. Jane's actions, after dragging herself out of the pond, appear to be spontaneous.