The Venus Butterfly is a MANUAL sex act performed on a female. If you can get ORAL squeezed in there, too, then you are either magic or fucking Plasticman. First thing, the Venus Butterfly requires plenty of lube. Place splayed hands together and approach the vaginal area. Index fingers will surround the clitoris. Third and fourth fingers will enter the vaginal canal. Pinkies will either slide in the anus or fold out of the way (depending on your female's preference.) Gently open and close your hands. This will force your hands in and out of the orifices/ orifii? also appearing as a fluttering butterfly. It will take some practice to perfect, but you will be remembered and thanked upon achieving any measure of adeptness.
Although thought to be either simple g-spot stimulation, or oral sex, you must have the concentration and dexterity of a puppeteer to perform the Venus Butterfly.