I think this mammal is a Fisher...
It was much larger than a Mink or Long-Tailed Weasel, with massive paws...
I was birdwatching in the woods along the river, and suddenly had the surprise and pleasure to observe this individual as it foraged back and forth along logs and brush piles, not too far from my position. I remained standing in place, and it went this way and that, sometimes assuming an erect posture on its haunches.
Found near the riverbank in the east central section of Iwen Park, in south Fargo, ND.
Animals were not caged. The weasel fell into the cart while attacking and killing the rat. Saw this little weasel out in the open, it has short tail and short legs.
Last photo the Otter is on the far shore line, Beaver in the foreground.