While very viable observations, you would be surprised. Because the shift from mostly gel to mostly spunk is very gradual, a lot of people wouldn't notice it. I am certain there is a specific name for this effect, but human beings in general will not notice slight changes like that. It's a reproducible effect, I believe. Download Audacity, for instance, and tell it to create a 30 minute sine tone at whatever frequency. Start lower for better results, I think. Not crazy low, just low enough to allow for the changes. Then set the sine tone to gradually shift up in pitch across the 30 minutes. Nothing dramatic. Maybe go up a fifth, A to E or something. Then while you are doing anything at the computer (Homework, just Facebook chatting, or even just reading.) have the sine tone start to play just loud enough that you can hear it, but it's not annoying. By the end of the 30 minute length, set it to loop. What will happen (most likely, as this doesn't work on some people who are audio sensitive and the like) is you won't actually hear any perceptible shift in the sound, and when the loop comes around, you'll hear a sudden drop in pitch, and only then realise. Same principle, only over a shorted period of time and a different medium. tl;dr People barely notice gradual changes, because your brain fills in the gaps until you pay attention.