Why Paul picks Spain for World Cup.

It's so obvious why Paul picked Spain.  Spain's box was closer to it when both boxes were lowered into the tank.

Here are stills from the video taken from the BBC.

Notice that Paul is in the right bottom corner of the tank. The box on our right is Spain:

And of course it's no surprise that Paul ends up in Spain's box:

You may wish to see the entire video.  Here is the link to BBC's video:

Click here for the BBC video