What did he say at 12:40 (video in description)

Can you crop the video? Probably not a lot of people here will watch 12 minutes of that video.

@chyna
you can just skip to 12:40

“using a rat filter” is what I get. (He can’t really be saying that, can he?) What do you think he is saying?

It’s called the Benham’s Top.

http://en.wikipedia.org/wiki/Benham's_top

@chyna regarding that…... he’s saying Red filter… he’s Dutch or something… yep.. just looked it up.. He’s Dutch.

I was just gonna watch it and skip to 12:40 but it’s fascinating and I’m gonna watch the whole things.

@cazzie is correct.