Cactus juice

Cactus juice is water from the inside of cactuses usually causing hallucinations as seen in "The Desert".

In "The Dessert"
In the episode "The Desert" Sokka and Momo both drink cactus juice and hallucinate. Starting with their eyes bulging, Sokka starts going crazy about cactus juice saying, "Drink cactus juice. It'll quench ya!  Nothing's quenchier.  It's the quenchiest!" Then, Momo starts flying in circle aimlessly, then plunging straight to the ground. Then, Katara takes away the juice. Sokka then asks "Who lit Toph on fire?" Later, as their walking through the dessert Sokka asks "How'd we get in the middle of the ocean?" Meanwhile Aang gets upset about not finding Appa and slams his staff into the sand which causes a mushroom cloud which causes Sokka to hallucinate even more saying the famous lines "It's a giant mushroom... Maybe it's friendly!!!!!" Then Katara suggests they keep moving and Toph and her leave Sokka and Momo. Sokka (still staring at the mushroom cloud) says, "Friendly Mushroom! Mushy giant friend!"