Martha hears music being played out on the street and goes to the window and looks down. She then throws a coin down to them. The violinist goes to pick up the coin from the sidewalk. However, the coin was already there in the first shot, before Martha throws it.
In a close-up at about the 0:51:30 mark when Mary Astor says "stuffed shirt" a large bit of spit comes out of her mouth.
At about the 8 minute mark (in the courtroom) the boom mic shadow can be seen moving on the far wall behind the actors.