I looked all over the internet and couldn't find anything with anyone wearing a falconry hood. I am disappointed. So I was GOING to just draw a sketch of Cas in a hood, but no. Partway through my brain went "THIS SHALL BE A MASTERPIECE! NO YOU AREN'T ALLOWED TO DO ANYTHING ELSE WITH YOUR DAY. YOU HAD PLANS? CANCEL THEM." And I made this.
I like to think that Cas's hands are tied together behind his back with his tie, while he's tilting his head up at Dean (or Sam, if that's your thing (or Dean AND Sam if that's your thing)), who is holding a riding crop. Because bondage can be quite fun.
The purpose of a falconry hood is to eliminate sight and sound, so that the falconer can focus the bird on a particular prey when they remove the hood. In the case of human bondage, while the hood is on it eliminates sight and sound and would focus the person solely on sensation (or scent, if you wanted to play with body oil, or wax, or food play). It would function as a blindfold that also muffles or eliminates sound.