Pen Thru Bill

Pen Thru Bill: A standard black Bic-type pen is shown and a dollar bill is borrowed. The pen is visibly thrust through the bill. Then the pen is slid across the bill seemingly tearing it, but when the bill is examined it is completely in tact. 

Both the bill and the pen may be examined with no clue as to the method. You are supplied with the special pen and detailed instructions. Any denomination of bill may be used.