Baffled I am. There are 3 faces that shoot "puffballs" (for lack of a better word), into the circle shapped cups mounted on the walls. What is the object? I can block them for a period of time, but not sure what the object is, in order to get the door to open?

The objective is to block all of the shots as the faces shoot faster and faster. Eventually they will stop shooting and the door will open, but if any of the shots gets through you have to restart the whole sequence.

This is made easier by the fact that the sequence will always be the same, so it's mainly a matter of developing the right key press pattern.