I think most of the succulent Euphorbias taste pretty terrible to mammals, if they don't actually burn. The naive squirrels may take a big bite at snout level, thinking how green and succulent the plant looks, but then they immediately spit it out. Here is a plant from that group that I recently put into well populated squirrel territory knowing this, and a couple months later the new kid on the block bit off a big mouthful, and spit it out on top of the mulch. I don't think they come back for more after they try it.
