It's gross-out time.

From Michael Dibdin's Ratking:

"A ratking.  Do you know what that is?"

Zen shrugged.  "The king rat, I suppose.  The dominant animal in the pack."

Bartocci shook his head.  "That's what everyone thinks.  But they're wrong.  A ratking is something that happens when too many rats have to live in too small a space under too much pressure.  Their tails become entwined and the more they strain and stretch to free themselves the tighter grows the knot binding them, until at last it becomes a solid mass of embedded tissue.  And the creature thus formed, as many as thirty rats tied together by the tail, is called a ratking."

The Wikipedia article suggests that ratkings are merely legendary.  Either way, yuck-o.

This was my first Aurelio Zen mystery.  While I was hooked on the intrigue (the mystery itself, the politics surrounding the case and within the police force) from this moment in the second chapter...:

Salvatore Iovino, their chief, a corpulent, vivacious fifty-year-old from Catania, had given a masterly performance.  Fulsome and vapid, laden with insincere warmth and hidden barbs, his introductory speech had nevertheless left no legitimate grounds for complaint.  She had spoken of Zen's "reputation," without actually mentioning that his abrupt departure from the Rome Questura in 1978 had been the subject of the wildest rumors throughout the force.  The two cases he had mentioned dated from the midseventies, underlining Zen's lack of recent operational experience.  He had referred to the transfer as a "posting," thus emphasizing that it had been imposed on him by the Ministry, and had called it a symbol of the historic relationship between Rome and Perugia, a relationship consisting of two thousand years of bitterly resented domination.

...Zen himself didn't completely win me over until close to the end.  But when he did, he did it in a big way.  He has a run-in with a horrible beast of a librarian who won't help him at all -- she makes him jump through hoop after hoop after hoop while she just sits there knitting.  When he finally has everything in order:

He handed back the forms corresponding to the last three months.  The woman scrutinized them in vain for further errors or omissions, laid down her knitting with a reluctant sigh, and trotted off.  As soon as she was out of sight, Zen took out his pocket knife and cut through a stitch in the middle of the work she had completed.

Yep.  Love him.