Before I started my PhD I conducted a 6 month internship at a young researcher’s laboratory working in Dresden. In short, it was the worst experience of my life.
Before I joined, he had told me that these 6 months would serve as a trial to prove I was ready to start a PhD at his lab, but when I solved the Visa problems and finally arrived to Germany, he told me that he had hired someone else for the same position and only planned to hire one of us. During the first months, he frequently yelled and belittled us, making us stay at the lab for several nights and weekends. He used to say that a scientist should push their body to the limit (even incurring into some bad habits) for the sake of science. He claimed that he had done so during his youth, and he was too old to keep doing it, because doing it so frequently was bad for his health, so it was now our turn.
Since I spent so much time at the laboratory and we were subject of the same mistreatment, I became very close to my colleague/competitor. He told me that he had started shaking because of his anxiety, and started taking pills to control it. As for me, I lost a lot of weight and was unable to sleep the few hours I managed to get into my bed. When the first 4 months were finally over, he graciously extended me the invitation to become a PhD student at his lab at the end of my internship, which I luckily refused. He became beyond furious.
He yelled, told me that nobody would hire me due to my immigrant status in Germany, and canceled my access to the laboratory, forcing me to ring the doorbell to enter the laboratory and not letting me work without oversight. Obviuosly, this made me vastly less efficient, but I did not care. Finally, he could yell and insult me all he wanted, but he was not able to fire me, as I would leave soon anyway. My partner told me that they were happy I would soon leave, as they could see how the pressure changed me.
The researcher offered the position to my colleague/competitor, who accepted. However, due to the terrible conditions, he quit during his first year. The last time I saw him he was still taking pills, and he had also lost a lot of weight. When I spoke with other people that also quit working at his lab, I realized that this was an recurring problem for everyone that worked with him.