All Hallow's Eve has its roots in religious practices; but nowadays, it's mostly an excuse to receive and consume candy, scare each other silly, and dress up in funny, funky, or spooky costumes in public without getting arrested.
But why should humans have all the fun? Cars want to get in on this, too!
Thankfully, some car owners extend the Halloween hijinks to include their automobiles. Here are nine pictures of some of the best vehicles.
1. http://curiousphotos.blogspot.com/2008/11/halloween-car-costumes-20-pics.html

Drop the top, Big Daddy, and lets go cruisin' on Halloween! The owner of this convertible obviously spent a lot of time on the details -- from the ghost art and bat rims to the windshield boa trim and the trunk lettering. All it needs is a horn that plays "Monster Mash."
2. http://www.flickr.com/photos/lenore-m/245189171/

This might be the most luxurious Halloween vehicle on the list. Note the faux-velvet seat covers and the window fringe on the back. It's an ideal car to take to the Halloween party -- or better yet, it can host a scary shindig by itself!
3. http://www.flickr.com/photos/puroticorico/1520709219/

Batman is a natural fit for Halloween, so why not spend the final day of October in the Batmobile? The exterior is tricked out much like the original, though it's unclear what munitions it has under the hood. But as you can see, it certainly has the capability to crush numerous skeletons.
4. http://www.flickr.com/photos/angryjuliemonday/4056033937/

Some cars (like those found in junkyards) are so frightening on the outside that you're terrified to pop the hood. The engine block on this Ford Mustang is scary, but not in a threatening way. In fact, studies have shown that cute Halloween characters help improve gas mileage.
5. http://www.flickr.com/photos/serpicolugnut/5089891068/

What's a giant spider doing on the hood of a perfectly spiffy classic car? Scaring the bejeesus out of parade goers, of course. And hey, the creature does have some advantages -- it's practically guaranteed to get slowpoke arachnophobes to move out of the way on the freeway.
6. http://www.flickr.com/photos/bilbord99/2993817945/

This car resembles a cross between a biker gang machine and a 70's horror film -- which is probably the reason it's so frightening. The orange lights, artistic jack-o'-lantern, and impaled monster mask on the antenna are unsettling, but the beer can is the most horrifying aspect. (Natty Light? Is that all they could afford?)
7. http://4.bp.blogspot.com/_mmBw3uzPnJI/SRAwL5CK6TI/AAAAAAAAVe0/OzQak4PUiG8/s400/halloween-cars-17.jpg

There aren't many scarier things than a Halloween car that can travel through time. But this tricked-out ride appears to be able to do exactly that. The four occupants are guaranteed to instill fear in the residents of any era -- except maybe for time periods when it rains constantly.
8. http://3.bp.blogspot.com/_gTJMEP-c2fo/SQrD4KAy1JI/AAAAAAAAHho/gAE6Io0UYVA/s400/halloween_car_2.jpg
The creators of this spooky car have pulled off a near-impossible feat: making a monster-laden hearse look kind of cute. The smiles on these creatures' faces make you want to join the party almost as much as the Cold Beers sign in the background.
9. http://4.bp.blogspot.com/_ax5ZIdFoW1U/SQ8bUpOwr3I/AAAAAAAAFOM/98QOhiZsehc/s400/halloween-cars-16.jpg

Sometimes, less is more -- and that's true with Halloween cars as well. Just hang a human arm out of the trunk, shatter the rear window, and place a hairy, scary mask flanked by two monster arms onto the back trunk. Voila! You're sure to scare other motorists and cause police to pull you over. (No telling what that may do to your auto insurance rates.)
Photo credits: curiousphotos.blogspot.com, L. Marie, puroticorico, AngryJulieMonday, TheodoreWLee, bilbord99, damncoolpictures.com, aautodealer.blogspot.com, curiousphotos.blogspot.com