furry friend in my compost bin!

I'm a bit new to gardening so sorry if this is a silly question!

So I went to put the veg in my compost bin and saw a ball of fur and a pair of black eyes looking at me!

I guess this would be a field mouse rather than a rat?  We live near farm land.

Was it just there for a nosey or has it found a new home in my compost bin?  Should I be worried?

You don't get furry friends in compost bins gardengnome

yikes I think it was a rat, it looked rather like this:
http://www.controlpestuk.co.uk/pests/rat%20catchers.jpg

Thanks I'll try that!
Can I ask a real dumb question, there's no way they can climb up the sides of the bin and bite you can they?!
I've just read that a wire mesh and some bricks round the bin stops them getting in, in the first place.

Jazzbyrd, behave 

People forget that the bottoms of bins are usually open and they can tunnel in, so a sheet of weldmesh will keep out anything. If the sides of your compost bin are fairly open, they'll climb through those so some tightly woven chicken wire or mesh inside will keep them out. I also put a metal lid on mind weighted with a big rock.

Unlike jazzbyrds trained acrobat rats, most rats will try to nip fingers if threatened so do keep the bin tightly sealed and turn it often to discourage vermin and ants.

They lurrrvvve trouser legs - even warmer up there...!!!

That would be worth doing & watching