But a new study suggests rats feel regret similar to the way humans do. Scientists at the University of Minnesota Department of Neuroscience realized such after monitoring rats' brains following a bad decision or mistake.

The researchers did so by offering the specimens an initial food reward as well as the option to move onto to an alternate food reward.

The scientists defined regret as "the recognition that you made a mistake, that if you had done something else, you would have been better off." When the rats declined the first food offering, and it turned out the second was even punier, the rats were dejected and regularly turned back to look at the choice they had passed up.

Mostly importantly, scientists were able to show that the same part of the human and rat brain -- called the orbitofrontal cortex -- lights up during regretful situations.

"The hard part was that we had to separate disappointment, which is just when things aren't as good as you hoped," explained Professor David Redish, lead author of the new study. "The key was letting the rats choose."

The study was published this week in the journal Nature Neuroscience.

The federal government killed 4 million animals last year
Washington (UPI) Jun 9, 2013 - Last year, Wildlife Services -- the federal agency tasked with protecting humans and their interests from the threat of animals -- killed some 4 million animals.

The death toll, according to the Washington Post, is as follows: "75,326 coyotes, 866 bobcats, 528 river otters, 3,700 foxes, 12,186 prairie dogs, 973 red-tailed hawks, 419 black bears and at least three eagles, golden and bald."

Critics argue the agency is overstepping its duties, and officials at the agency haven't been able to explain why the casualties of their services -- the number animals they kill -- varies so wildly from year to year. Over the last decade, the total has swung from 1.5 million to 5 million and back again.

The majority of killed animals are native species, and most of them are killed to protect the assets of a ranchers and farmers. Often, coyotes and foxes are killed en masse on the behest of an overprotective cattle-owner.

The issue seems to be not only the grotesque number of animals killed, but the severe lack of transparency and accountability at the agency.

"[Wildlife Services is] one of the most opaque and obstinate departments I've dealt with," explained Rep. Peter A. DeFazio, D-Ore. "We're really not sure what they're doing."