Yes, the thing you take a bath with. It comes from a squash. I am not sure if this is spelled correctly, but the Chinese call it "si gwa". When picked young, it is a squash that is popular in many parts of the world. Allowed to get overgrown on the vine and then dried, the network of inner fibers of the squash fruit becomes what we use as a loofah (lufa, loofa, many spellings for the same thing).
I am growing some this year, too. I am not sure whether the leaves are poisonous, but if the squash is used to make soup (and I have eaten said soup), I am sure it's pretty similar to other squashes. It kind of looks like a zucchini when it's growing, and make sure you have a STRONG ladder or trellis or "teepee" to hold it up.