When Meryl goes into the women's bathroom, get to the last stall in five seconds or less. During an FMV sequence you will see her with no pants.

OR

When you go into the vent shaft and look into Meryl's cell, she will be doing sit-ups, then climb out of the vents and go back up into them look back into Meryl's cell and she will be doing pushups, repeat this a third time and she will be doing leg presses, Finally repeat again and the cycle will start over but this time Meryl won't have on any pants!