"Rats are capable of feeling regret about their own actions..."

"... an emotion that has never previously been found in any other mammals apart from humans."

Before clicking, see if you can think of an experiment that would test a rat's capacity to feel regret.

Meanwhile, I'm picturing a rat singing "My Way"...  

Regrets, I've had a few/But then again, too few to mention/I did what I had to do/And saw it through without exemption...

That actually is probably the way a rat thinks. (Hey: The Rat Pack!)

I'll bet you think I should regret writing this post. Non, je ne regrette rien.