1.
After Betty and Rita have entered Club Silencio and taken a seat they watch the Magician start his performance. Betty places her purse in the seat to her left at a well perceivable position. There it rests for the time being. The seat behind Betty is sitting up.

2.
Right after the Magician announces "It is an illusion!" the purse has suddenly changed its position in the seat. We can only spot part of the handle. In addition, the seat behind Betty's is now folded down.

Did someone come from behind messing with Betty's purse?

3.
After a close-up of the Magician we see Betty shaking violently. Suddenly a dark, rectangle object appears behind her back.

Could it be a cushion to help Naomi shake herself and protect her back?

4.
The Magician hides in the air and Betty calms down. 
Here is a twist - the purse is back in place and the seat behind Betty is in upper position as it was in the beginning (1). 

5.
After Rebekah has entered the stage there is a last shot of our couple. Again the setup is altered. Now it resembles (2), except for this strange object present behind Betty.

Finally Betty discovers the blue cube in her purse...

Additional note
Watch the couple behind Betty and Rita. Does one of them hold a brown paper bag, similar to the one the Bum drops the blue cube in at the end?