Reptiles shed their skins frequently as they grow (scientifically ecdysis). As the old skin prepares to be shed, oil builds up between the old and new layers, making the reptile look dull in colour, and in snakes this creates a film over the eyes, interfering with their vision and making them vulnerable to predation. The animal may also become lethargic and remain in the same area. When it is ready to slough the reptile rubs its jaws on a log or stone to loosen the skin, which then peels off, inside out. These cast skins are sometimes found in the grass.
Play detective. Find out which animal shed the skin you have found. A long thin slough with small dorsal scales and broad belly scales will belong to a snake. Hold the skin up to the light. You may be able to see the animal’s body pattern and discover which species you have found. Look for vertical bars along the sides for a Grass Snake or a broad zigzag across the back for an Adder. An unmarked slough with tiny, uniform scales all the way round comes from a Slow-worm. Snake sloughs are usually whole but lizard sloughs are often found in fragments. In Common Lizards you can sometimes find the whole slough in several pieces over a small area, including complete sloughs of the feet, rather like a transparent glove.