The labels on the boxes read as follows:
[box 1] nails
[box 2] screws
[box 3] nails and screws
To gain the information you need to move the labels to the correct boxes,
you may remove a single item from one of the boxes. You may not look
into the boxes, nor pick them up and shake them, etc.
Can this be done? If so, how? If not, why not?
[Edit to add solution.]
[Edit again to explain.]