Most wild thing I've heard lately is the cognition theory that most of what we perceive is surprise.

The thumbnail sketch of the idea is: we know from glucose uptake studies that there's basically no way our brain is actively synthesizing every sensory stimulus at all times. The hypothesis is that the brain creates a sort of "predictive map" of reality (which is what we perceive), and then uses sensory stimulus to listen for variance from that predictive model. So most of the time, what you perceive is a hallucination of reality that maps close enough to what's going on, and only when sensory input starts to deviate from that predictive model does the brain dedicate the resources to "read" the sensory input and meld it into an update of the prediction to match reality.

There was a Kyle Hill video on this recently. He also notes that there's an easy experiment you can do to observe your brain doing sensory fusion: touch your finger to your nose. We know, physically, that the signal from the finger takes way longer than the signal from the nose to reach the brain, but we perceive the two touches as a single instantaneous event that happens at the same time.

I've had these - or rather, been able to see them - since I was a child out on playing on a large, empty field of fresh snow. I originally assumed they were little ice crystals freezing on my eyes (since it was very cold, and I was often outdoors in the snow when I saw them). Some time in my teenage years, I learned what they really were, which is even more fascinating. Once I notice them, I can pretty easily tune mine out, like one of those optical illusions where you can consciously switch between perspectives. (I have some floaters, and can normally do the same thing with them as well.)