What is mud?
It might seem obvious, but just to clarify, mud is the term given to soil that is mixed with water. Mud made from healthy soil is rich in nutrients and therefore mud of all different types has been used in ritual treatments by humans for many thousands of years. Today, you can still treat yourself to mud treatments, albeit the mud isn’t the soil-from-the-woods type and is slightly more exotic.
Mud that is made from healthy soil will be dark in colour, free from foul odours and rich with microbe life. This is the best kind to let your dog loose in.