You're allowed but not bigger than...

The phrase "rule of thumb" is derived from an old English law which stated that you couldn't beat your wife with anything wider than your thumb.

Rat vs Camel

A rat can last longer without water than a camel.

King's Cross

King's Cross, the place made famous in the Harry Potter Book Series, has a special meaning to J.K. Rowling, it was where her parents met.