This was seen is the main road between the cities of Corrientes and Resistencia in Argentina. The cities are separated by the magnificent Paraná river and the road connecting the two is truly busy. It was while driving on the motorway that we spotted this oddity. We almost overlooked it but then we spotted something wrong. Can you see it?

It is not easy to see what is wrong! Here is another picture taken when the tractor got closer and with a different angle:
Usually, tractors move on four wheels! However, these gentlemen were driving -rather unconcerned- on three by some miracle of engineering equilibrium!