Why do their eyes pop out? If seen this in several series now. When your blowing on something really hard, your eyes come popping out. Is this some sort of symbolism?

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This is a common trope, not specific to anime. It can be seen in a lot of western cartoons.

The increased air pressure, that is created when blowing very hard, creates a force pushing outwards from your breathing cavities and connected airways. Technically, mouth, nose, ears and eyes share the same complicated pathway, so you could blow your eyes out, if you try hard. The trope in question is just an exaggerated example of it.