I'm having flashbacks to Skyrim. Developers were puzzled how players got a bounty even when no one was around and discovered that chickens were reporting crimes.
I'm reminded of CK2, where there was a big performance drop when the India DLC was released. The reason: all of the Greek and Armenian characters were constantly checking if every other character in the game was someone they would like to cut the balls off of, adding more characters caused an exponential increase in the time that check took.
And they're pretty protective of them, I remember learning that one the hard way. Accidentally killed a chicken in Riverwood and suddenly the whole town was out to kill me for de-fowling them.
Explains my lag so well. Everything freezes. Except my controllable character. But everyone else is standing still. I can't interact with anything. Can only wait for the game to catch up. Was never a problem until I got to baldurs gate.