1 star cuisine

I've noticed recently that a lot of takeaways and restaurants have a sign on their door with their hygiene rating, ranked from 1 to 5 stars.

Whenever I see a sign with less than 5 stars, I can't help wondering what it takes to lose a star.

Is a cockroach worth a star? Or does it take a bunch of roaches? And what about rats - a rat's bigger than a roach so it wouldn't be fair for one takeaway to lose a star for one measly roach and another place loses the same number of stars for a rat.

Oddly enough it wouldn't bother me if a place had only 1 star; I'd probably be standing in the doorway munching on a salmonella infested, rat dropping laced burger while wondering how they lost their stars...