I just go with whatever pops up in my head at the time. Usually I try and take a key element of the chapter and create a short little phrase that paints a vivid image about what the chapter's about
For example, a chapter about a certain manipulative, snakelike individual and a draconic businesswoman would be called "Snakes and Dragons"
One that features a fight with a werewolf is called "Tooth and Claw"
Another one where the MC has an emotional breakdown is simply called "Panic Attack"