As arnswine said, they are to let water out. If you plug them up you'll have more rust than you ever dreamed of. A lot of the rust on old vehicles is caused because drain passages got plugged and wouldn't let water out.
Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.
| 
