Williams Exhausts

Most cars have cooling vents or holes for the oil and water near the back of the sidepod. Some are nicely crafted and made like gills like Ferrari and Toyota, and others are more basic and are literally just holes at the back of the sidepod. Some cars have the hot air 'chimneys' like renault and Williams on top of the sidepod. In cooler temperatures and in friday practice/qualifying Ferrari don't need to have the gills and replace them with 'closed' pieces, like the car had at its launch.

Powerhorse is correct, both halves of the pipe are exhaust pipes, with a bit added int he middle for efficiency, so it looks like 2, but is really just 1.

Also Imran, yes at the beginning of the season after Toyota launched this years car, F1 Racing magazine commented that they have basically copied the F2002, with the exhausts, and other general parts of the design.