Arm-deep-fisting refers to a specific act in extreme BDSM and anal play, where one partner inserts their arm or hand deeply into the other partner's anus. This act is considered highly advanced and involves a significant degree of physical flexibility, as well as a strong bond of trust between partners. It should be approached with caution and only under mutual consent, as it carries considerable risks including injury or perforation if not performed correctly. Due to its extreme nature, this activity is not for everyone, especially those who are new to anal play or BDSM activities.