I found a clip at 3:14. Inspectors walk beside it while the engine thinks it's running at speed listening for clanks and grinding. Probably re-oiling before each pass back and forward.

The position of the radius rod would indicate this "Santa Fe" type is in reverse motion.

Anyone ever felt like that? For us, wouldn't be like spinning wheels on a greased track, but instead would feel like running in place and getting nowhere. At work or at home or anywhere.

That just seems to be all kinds of dangerous to me. I know that traction isn't great with steel on steel and that greasing the rails negates the little traction there is, but it seems to me that a heavy locomotive will eventually wear through the grease and get traction. Maybe the front wheels are chocked? In any case, I'm sure that there's nothing on the rails in front of it and this is something they've done before. I'm sure if it was so risky we would have read about how they spectacularly crashed a locomotive into something.