Spoiler

I'm guessing this is a question on classical conditioning, where people are being asked to pair the unconditioned stimulus, the saliva, with a neutral stimulus, the water. Over time, if something like this were to continue, the backwash would become a conditioned stimulus, making you fear drinking the substance. I may be wrong though, been a while since I studied psych stuff, been having to get back into the groove of it in a class that uses applied psych in teaching.

That's not quite the application for it, but it's possible to do something along those lines if you have the time/effort/lack of morality and ethics to do so

This was more to do with how when something that one second is residing inside your mouth without being gross, the next second it causes them to go 'ew'. The rest of the extract from the book was to do with how younger children haven't developed a sense of disgust properly, which is why they are able to eat things like spiders with wanton glee. There was also a smaller study done where they dropped sterilised insects into milk/juice which would ordinarily stop most people drinking it but the kids just chugged that shit down >.>