Muffing may involve inserting one or both fingers into the inguinal canals. Locating these canals can be difficult, as they’re surrounded by flesh. Bellweather suggests people can find the inguinal canals by feeling upwards and behind the penis. While the entrances are small, roughly the same diameter as a finger at first, they will stretch with repeated muffing. As the inguinal canals are so small at first, newbies should start slowly and take care.
Muffing feels good because the canals contains the ilioinguinal and genitofemoral nerves that make touching your genitals pleasurable. The deeper a finger is inserted, the better it should feel. However, you should avoid fingering too deeply, or you could potentially cause harm. There are also psychological reasons why pre- or non-op trans women who feels no real connection to their penises often find muffing sexually gratifying. Some trans women who get gender reassignment surgery say they miss muffing because fingering the vagina, which is naturally lubricated, can be much messier.