Keep an eye out at yard sales or for sales at local pet stores for aquarium filter motors...they make great "bubbling" potions and concoctions in flasks and jars. And a cauliflower with a few strategic cuts here and there looks remarkably like a brain when you put it in a big jar with colored water (add a few tbsps of milk to make the water murky...adds to the drama if you can sort of see it, sort of not). And a fennel bulb (see link
Fennel - Wikipedia, the free encyclopedia) looks eerily like a human heart (roughly the same size, and has those things coming out the top like the big vessels of the heart, just cut off the leafy stuff) when placed in red colored water, really looks creepy. Sorry I don't have pictures, but that was before the digital camera.