I always remembered the original saying is that human will consider things "animated" when it's above threshold (24fps or whatever).
Telling 24, 30, 60 apart is very trivial.
As for 120fps, you need to keep in mind that playing a real-time rendered computer game is a totally different beast than playing back a steady video. There are lots of other factors involved. Some headroom in FPS makes lots of difference due to various other things like jittering (judder?), input delays, response time etc. (also it's possible some people simply can tell 60/120 apart, even by just watching a video.)
60hz vs 120hz is also obviously apparent if you have them next to eachother (when using multiple monitors, for example). Just jiggling the cursor around or scrolling a webpage makes the 60hz look almost stuttery in comparison. Same goes for UI stuff like the animated dropdown of a menu.
Another big difference is that motion in video frames are smeared because of a (simulated) shutter speed. Whereas a video game every frame is perfectly crisp. This makes a huge difference on the smoothness experience.
Telling 24, 30, 60 apart is very trivial.
As for 120fps, you need to keep in mind that playing a real-time rendered computer game is a totally different beast than playing back a steady video. There are lots of other factors involved. Some headroom in FPS makes lots of difference due to various other things like jittering (judder?), input delays, response time etc. (also it's possible some people simply can tell 60/120 apart, even by just watching a video.)