From a survivability standpoint, a rat is a real piece of work.  It's no wonder they have such a reputation as survivors during times of peril.  Fire, flood, famine, disease — and don't forget getting out of tough places.  When it comes to getting into situations where almost any other animal would perish, consider the following.

You know that classic rat complaint, "Ooh, those ugly naked tails!"?  Presumably, by "naked", they mean "skin"?  Well, surprise; it's not skin.  They're scales.  And very sharp ones, pointing backwards.  They can really dig in when pushing against something.  It actually acts as a fifth leg during times of crisis.

Their tail is also that exact length for a reason.  Watch a rat balancing on the edge of a big bowl or box.  As long as the tip of its tail can touch the ground behind him, he'll lean way down into the container.  But as soon as the bowl is high enough and his tail loses touch with the ground, he becomes much more cautious.  What this is basically telling the rat is, as long as the container isn't any deeper than his tail, he can get back out.

Their tails are also much stronger out in the wild than what our household pets exhibit.  I started training Bumpkin at an early age to swing herself up when held by her tail, and she can now, at two years old, swing herself up when I'm holding it a third the way down, a remarkable feat considering that a normal pet rat immediately gives up and just hangs there looking puzzled.

They don't have "claws", they have fingernails.  Claws and talons, on a microscopic level, are relatively blunt.  A rat's fingernails, however, rather than coming down to a point, use the concept of width, instead, providing much more surface to grip with.

Their rear feet can turn around and act as hands, helping to pull themselves out backwards from a tight spot.  This is a real key point.

They can also leap much further than most people probably think.  Two feet isn't any big deal to an adult female.  And they can be as clever as any animal alive when it comes to breaking out of their confines.  If you've heard that story about mice, and how if they can squeeze their head through, they can squeeze the rest of their body through, this is also true with rats.

They also do something fairly clever when they fall.  Like a cat, they turn themselves rightside-up in mid-air, but, unlike a cat, they don't try to land on their feet.  They basically just go SPLAT! and land on their fat bellies.  They'd break their limbs if they tried to land like other animals.  But they'll land on their tummies like it's no big deal, pick themselves up and trundle right off.  I'm speaking of carpet, of course.  Cement might be another matter.

I recently picked up a new female that shows a trait I hadn't seen before.  When she's in any kind of semi-precarious situation (hand, shoulder), her rear legs automatically 'pontoon' themselves by going almost straight out from her body.  Most rats will splay their legs a bit, of course, just to keep their balance, but this one is really unusual.

The Darwinian scenario states that suddenly the platform a bunch of rats are standing on shifts violently during the earthquake or storm, throwing all of them to their deaths, except for the one with the 'pontoon legs' who manages to get a grip on something.  Eight feet away, the same thing happens, and elsewhere in the world.

Then the survivor meets another 'pontoon' rat, and, a million years from today, all rats have pontoon legs.

Evolution never sleeps.

Add to all of that an animal who can go longer without water than a camel and can basically survive on cardboard, and you've got one serious survivor.