Aren't the intervals supposed to be random to be an effective torture method?
I think you're thinking of a different torture.
The fixed interval is correct. It's similar to having the person watching a steady, continuously flashing lightbulb. It disorients the person and messes with their sense of time. They know (or realize) that the water is dripping on them at a regular interval, yet perception is telling them otherwise.
Don't ask me how I know this...
We do it the same way, a drop of water at a time on the forehead...You tie a person up and hold them still, and at fixed intervals, you drop cold water on her forehead.Like hell it's wakin' her up—if anythin' it's puttin' her classically to sleep!?Oh....... What the heck are we doin'?Tell me about it.If that's how it's going to be, let's try out a certain famous torture technique.ZzzzZzzzTorture?It seems plain enough, but it's enough of a torture to drive a person mad.It's not the technique's fault. Reimu's just too brazen.