Hi, I observed a strange behaviour in my cell lines I had never seen before. Those are stable lines from Ovarian cancer (line's name: HEY) and from Prostate cancer (line's name: PC-3). Both lines were put in culture from -80°C the day before and after 24h they showed the presence of black bubbles around the membrane moving and growing. The Ovarian cells were myco negative and reached the confluency then with any problem getting the normal morphology. Do you have any explanation or advice, such as a kind of contamination I have missed from literature? Or could it be a normal cell's behaviour trying to stick to the flask or getting a connection with each other? Thank you.