A circus owner walked into a shop to see everyone crowded around a table watching a little show.
On the table was an upside down pot and a duck tap dancing on it.
The circus owner was so impressed that he offered to buy the duck from its owner. After some wheelin' and dealin' they settled for $10,000 for the duck and the pot.
Three days later the circus owner runs back to the shop in anger, "Your duck is a rip-off! I put him on the pot before a whole audience and he didn't dance a single step!"
"Hmmm...." thought the duck's former owner. "Did you remember to light the candle under the pot?"