On one occasion I smoked some Saliva extract on LSD, and it was an entirely hellish and revolting experience, yet very powerful and interesting at the same time. When I realised that what was going had something to do with me and my brain, these infinite hard layers, seemingly from infinity, would bend in on me from the front of my vision, and over and over again, as they passed through my brain, I would feel them rake through me as physical pain. Really revolting actually, glad it doesn't last long in real world terms, although it definitely felt long enough at the time.