I think it has to do with the adrenaline? Like we've all read that dogs can smell/sense fear and that's why they react differently to different people. Maybe a rat that knows it's safe doesn't make it exciting. But we know a plastic bag doesn't either, and Asha goes nuts for fast cat... who knows.
Had a pair out in the front yard one day off leash (a very stranger unfriendly pair) and the Animal Control truck comes down the street and stopped in front of my house. Guy stopped, got out and walked onto the edge of the property all smiles / full of confidence and squatted down low right at the edge of the yard to 'greet' the girls.
They ran up to that guy nubs wagging like he was their long lost soul mate. No barking, no growling, just ran up to the guy like they had known him forever and expected an ear rub or better from him...
He pulls some jerky type treats out of a pocket and DID ask me if he could give them to the girls (girls crapped their fur pants once they saw this guy pull out those treats).
Told him to go ahead and then watched as the girls both gobbled them up instantly as he rubbed on them...
We got talking and I explained to him how I 'thought' I had those girls pretty well bait trained (not to eat anything out in the yard) and trained to NOT take food from strangers as well and he just demonstrated to me how no. I did NOT have those girls properly 'trained' for any of that stuff.
That Animal Control guy - His body language, his actions, everything about that guy just instantly clicked with those girls of mine.
I would be willing to bet money that that particular random stranger AC guy could have opened the side door of his truck and the girls would have eagerly hopped in to go for a ride with him.
Kinda like a barn hunt! 
