1.
Betty & Rita entering Club Silencio, taking a seat and watching the Magician start his performance. Betty places her purse on the seat to her left in 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!" causelessly the purse has changed its position on the seat. We can only spy a part of the handle. In addition, the seat behind Betty's is now folded down.

Did someone come from behind reaching for 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 Betty shake herself and protect her back?

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

5.
After Rebekah enters the stage there is a last shot of our gals. Again the scenery 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?