Final answer:
A properly fitted horse riding bit should lead to one to two small wrinkles in the corner of the horse's mouth, indicating correct positioning and pressure.
Step-by-step explanation:
A correct fitting bit for horse riding will leave one to two small wrinkles in the corner of the mouth. This is a commonly used guideline to ensure the bit is not too tight or too loose, which can cause discomfort or lack of control. The wrinkles indicate that the bit is sitting in the correct position within the horse's mouth, pressing appropriately against the corners. It's important to always consider the individual horse's anatomy and responsiveness, as some may require slightly different fittings. Furthermore, the presence of a demarcation line on the skin, as mentioned in the reference information, is unrelated to fitting a bit but indicates areas of skin that have or haven't been exposed to sun.