Ah ha; it's sort of like a fat ferret. Cute, but devious.

Pine Martens are beautiful. I've seen them several times in the US. Squirrels are terrified of them--they are apparently very efficient hunters.

Apparently they're good for red squirrel conservation, they'll hunt the invasive grey squirrels but not the long-suffering native red squirrels.

Wow, I didn't know that. The first time I saw one was up in the Enchantment Lakes in Washington State. We came around a corner in the trail and heard the squirrels making a furious racket high up in the Douglas Firs above us. I remember thinking "hey, we can't be that scary, what gives?"

We turned a corner around one of the Dougs and there was a big Pine Marten scrambling up the bole of the tree, chasing squirrel for lunch. Mystery solved!

Never heard the name marten before, weasel is ised more often i guess. https://en.wikipedia.org/wiki/American_marten?wprov=sfla1

Yes but a European Marten of which he speaks is much bigger that a European weasel.

https://en.m.wikipedia.org/wiki/European_pine_marten

This is the real culprit, in fact.

https://en.wikipedia.org/wiki/Beech_marten

Haunting people making noise at night in old houses is also a common hobby (but somebody must to run after the yummy mice).