Cannabis can cause mild hallucinations. In my experience these usually materialise in the form of sounds. Sometimes when I am lying in bed I sort of hallucinate music, often it is like nothing I have ever heard before, like some experimental techno, and occasionally I dream music I have never heard. Sometimes when I close my eyes in bed I also have visual hallucinations, like fractal patterns that morph into random scenarios, like a mountain scape, or people, or anything really. I don't know if they can strictly be called hallucinations, although one time in my early days as a toker I woke up in the night and there was a blue face floating in front of my eyes, not with very distinct features, more like a computer drawing sort of thing. Around 6 years ago I took a bus from Pushkar in India to Udaipur overnight, and for the journey i took along a bottle of "full power" bhang lassi, a yoghurt drink made from marijuana leaves that is legal in that part of India. The noise this old bus made on the bumpy road turned into music, like this minimal electro mix, quite possibly the most enjoyable bus journey i have ever taken.