Yesterday I completed a double-blind test on myself. I missed some spots applying sunblock.
The subject did not know whether he missed a spot or not. The arbitrator did not know which spots were missed. However upon collecting experimental evidence, spots were missed. When compared to back-calculated extraneous features, the length of the swim-suit vs expected length of swimsuit, after correcting for body positioning, conclusions were drawn with high certainty.
A) sunblock works
B) the area between knee and mid-thigh was insufficiently sublocked
QED