Wolf's-milk is a term used to refer to the sap of certain plants that are known to have toxic properties. This colloquial term is used to describe the milky sap that oozes from the broken stems, roots or leaves of plants like Euphorbia, which are usually found in arid or semi-arid regions. While the term "Wolf's-milk" is widely used, it is also known by other names such as milkweed, spurge, rubber vine, devil's milk, and goat's rue. These synonyms are often used interchangeably depending on the location and the species of plant being referred to. Regardless of the name, it is important to always respect the toxic properties of these plants and handle them with caution.