Attached is a brainteaser which I think is cute. Too late for the April fool's day but still... 
Some comments: three consecutive scans of the same sample were taken in this order: scan 1, 2 and 3. Duration: 30 minutes per scan.
 
If these data look unusual to you please tell us why and what could've happened in this experiment. 
 
Those of you who send first three correct answers will be acknowledged!
 
Anatoly