As another poster said, it's all about the dosage. Anything can be a poison. Even water - there have been several cases of people dying from drinking too much water, some side effect of taking ecstacy - they felt thirsty however much they were drinking.

Vitamin A is a classic: Too little, and you get blind and your feet start bleeding when you walk. Too much, and you get blind and your feet start bleeding when you walk.

I'm going to go out on a limb, just to be contrarian, and say that no amount of perfluorodecalin is poisonous. You can immerse yourself in it, fill your lungs with it, fill your entire digestive tract with it, and replace a significant amount of your blood with it. It is completely inert to biology, and is readily permeable to atmospheric gases.

[0] https://en.wikipedia.org/wiki/Perfluorodecalin

Thanks, I forgot the details since this happened 10 years ago, my point stands that the juice sellers did not warned about this side effect.