Continuity mistake: When Walter is watching the fire go through the electrical system in the walls of the kitchen, watch the blender. One shot shows thick, chunky, white/orange stuff flowing out over the edge of the counter. The very next shot shows the blender toppled, but very clean. There is no trace of the chunky stuff in the blender or on the counter.
Continuity mistake: When Walter watches the electricity disappear in the wall, you can see about six tiles fly at him, but only three or four missing on the wall.
Continuity mistake: When Walter is getting the water from the stove you see only one bucket. When he gets upstairs with the water he is carrying two buckets.
Continuity mistake: When Walter gets catapulted through the window and into the plaster tub he lands on top of the window curtain. He raises his head, now covered with plaster, but not with the curtain. When he stands up we see his head and entire body thoroughly and completely wrapped in the plaster soaked curtain.
Continuity mistake: After the first full day's work is done, at first, there isn't any scaffolding, but when Anna comes home late at night, there is heaps of scaffolding.
Continuity mistake: When the owner of the house greets the young couple at the door, her drink is in her right hand, but once inside her drink is now in her left hand.
Continuity mistake: When Walter is hanging from the staircase after its collapse, Anna is about a foot back from the edge of the steps when she first approaches. However in the closeup shot we see that she's now on the edge and on Walter's fingers.
Answer: It was Jane Fonda.