They said in the article that it was a "submission" gesture.
It is in mice....
Ya know, this kind of suggests how clever rats are in a way...they clearly need a lot of tuition about "what to run away from".
I guess mummy hadn't got to leopards in the curriculum.
Or this is the rat whose little brain isn't very good, and natural selection will soon take care of it.
Ratlets are so CUTE!
My first Siamese was like that with my horse...utterly fearless.
He bent down to sniff her the first time they met, and she stepped right up to sniff back. Then he snorted in amazement, as horses do, and knocked her arse over teakettle.
Instead of being afraid, she picked herself up, marched right up to him, glared at him, and swatted him one across the nose...this when she was barely bigger than one of his hooves!
After that, the question of who was dominat in that relationship was settled....but she was very affectionate to him as long as he was careful to acknowledge her dominance.