Very strange behavior when creating new files and writing classes.

Hello,

As you can see I have created a python project folder with a few .py files. I finished with food.py and animal.py - no problems there. After that I started working on birds.py. When I wrote class Bird(Animal), PyCharm did not recognize that Animal is not implemented and it didn't ask me to implement it. I also saw this thing "Analyzing..." and I don't know what it means (first screenshot). After rebooting PyCharm, everything works as expected (second screenshot). This is happening for the n-th time. Why is that so?