Trees

Because you literally feel like that. It feels like you went up one level, and now everything tastes better and looks better and is funnier. You suddenly understand so much more, you are even smarter (if you weren't so damn slow at the same time). No joke is too complex for you.

And you feel like everybody who is high at the same time is on the same level as you. At this moment, you are all one awesome group of people who advanced to a higher level for a while. You have all your inside jokes and mannerisms and you all understand each other in that state. Even hooking up is easier because you are all together in this. And when you come down, you literally feel like you come down one level of reality.

Man, I bet this is why all religions talk about paradise being heaven. All those religious dudes probably got stoned from various shit and then came up with the idea of paradise being on a higher plane of existence.