First couple days were not that bad. Not particularly good, but nothing too bad. Like people weren't too friendly but neither too hostile.
There was, though, some casual heated discussion here and there. As I met some people more closely I began to see a trend: Everybody hated almost everybody else. One developer openly told me in our first conversation something like "You'll notice few people talk to me... Everyone hates me here.". Then somewhere else some shouting erupted for a few minutes, but nobody seemed to pay too much attention to it.
I saw someone get up from their desk, go to someone else and instead of normally asking whatever question they wanted to ask, start shouting their question. "How can it be that something something?!!! This is totally unacceptable!". Nobody even looked up from their screens or anything. It would turn out that was the way they always communicated.
We got a meeting with the whole team. Ah, no, not the whole team, just half of it. Why? - I asked. "Oh, we tried that but we can't have the whole team in one meeting because there are... conflicts and we end up not doing anything productive."
A few days later, I get called into a meeting with 6 other people, just to generally estimate a few tasks and discuss some of their details. After about two minutes or so, two people are arguing which ones are the tasks that we need to discuss. Things escalate and they are shouting while the rest watches calmly. I don't even know what to do or where to look because none seems to react at all to this. After some 15-20 minutes of this, the meeting is cancelled. People just stand up and return to their desks. I ask one of them if this is normal. "Yeah, pretty much."
I tried really hard and stayed there for more than 1 1/2 years. The only thing I have from all that is a lot of awful anecdotes about awful people.