Empathetic Rats

So I'm back to rats after all ;-)
The following NYT article is based on an article in the 12/9/2011 Science, which has gotten a lot of air play.  I've read the original article on watched the video narrated by one of the authors (easily Googled).

Rats to the Rescue in Cage Experiment

By SINDYA N. BHANOO

Published: December 9, 2011

The researchers placed a free-roaming rat in an arena with a caged rat. Over the course of several days, the free rats realized they could nudge open a door and release the caged rat.
After figuring this out, they did so repeatedly, day after day.
“They then did what we refer to as a celebration,” said an author of the study, Peggy Mason, a neuroscientist at the University of Chicago. “The trapped rat runs around the arena, and the free rat appears excited and runs after the trapped rat.”
That behavior alone is not enough to show that rats are empathetic, she said. The rats could be releasing their caged cohorts simply for companionship.
So the researchers changed the setup: when the free rat released the caged rat, the caged rat went into a second arena, and the two were unable to interact.
Still, the free rats released the caged rats, day after day.
Then the researchers placed a free rat in an arena with a caged rat and locked-away chocolate.
The free rats were just as likely to free the caged rat as they were to liberate the chocolate and eat it. Moreover, when they got the chocolate they almost always shared it; on average, they would leave about one and a half out of five pieces for the caged rats, Dr. Mason said.
There was also a difference in the behavior of male rats and female rats.
“The females, once they open the door, they open the door every day, and within a few minutes,” Dr. Mason said. “But the male rats would occasionally take off a day.”

My reaction: 
The observations are very interesting, but I suspect that the authors have much less direct experience with lab rats than my 45 years of handling, caring for and teaching them.
Lab rats (unlike wild ones) are highly social and friendly beasts who have had a lot the the caution and aggressiveness of the wild ones bred out of them (and lab rat that bites a handler is likely to be eliminated from the gene pool immediately).
Unlike wild rats, domestic ones will move into open areas, although they will look for nooks and crannies to hide in if chased.
And a standard method for measuring emotionality in rats is defecation.
A frightened rat will not only freeze; it will defecate.
A frightened rat will leave droppings on the floor of the enclosure; a terrified one will leave soft, sloppy droppings.  If the authors' rats had in fact been 'terrified' (their description) by venturing into open spaces it would have been very obvious.

So, the more parsimonious (and less anthropomorphic) explanation is that the opportunity to socialize with other rats is a reward, and is sufficient to account for all the the described actions.
Another issue is that handling by caretakers immediately after a session is also reinforcing (rewarding), and requires careful experimental control to avoid bias.
The fact that the observed behavior is consistent with the phenomenon of empathy doesn't mean that this is the most likely explanation.
First one must eliminate simpler alternatives (shave with Occam's Razor).
This they have not done.