What simulations do the jurors perform?

1) 4th Juror explains that, on the night of the murder, the boy bought a uniquely carved switchblade knife identical to the one used in the murder. The boy claims that he lost it that night, before coming home to find his father dead. 4th Juror presents the death weapon, the “only one of its kind;” 8th Juror surprises the others by presenting an identical knife he had purchased in a pawn shop two blocks from where the boy lived a few nights prior, shattering the claim that the knife was unique and identifiable.

2) After a brief argument, 8th Juror brings into question whether or not the downstairs neighbor, an old man who had suffered a stroke and could only walk slowly, could have gotten to the door to see the boy run down the stairs in fifteen seconds, as he had testified. 8th Juror recreates the floor plan of the apartment, while 2nd Juror times him, and they conclude that he would not have been able to reach his door in fifteen seconds.