The Brown Rat or Common Rat is also called the Norway Rat although it came from Asia rather than Scandinavia and has spread worldwide. It can be greyish brown.
The tail is as long as its body.
The Brown Rat climbs well, both trees and houses (although not as well as the Black Rat, also called Roof Rat in America).
Baby Brown Rat
Juvenile Brown Rat (the young are greyer than the adults)
The rat that liked escargot - see link below
Rat collecting snails
Rat and Squirrel