For a car, a tombstone is lightweight. Cars are very strong, you see, so something heavy like a tombstone is no match for them. All cars find tombstones to be light and easy to transport.

What do you wish you had to transport this tombstone? Oh, that’s right, a car. So you need some kind of car loophole (かる). If you had a car, this tombstone moving business would be no problem. To cars, tombstones are naught but lightweight pebbles! But the rules say you can't use cars to carry tombstones, so you need to find a car loophole.