Nipples are second only to the male cock as sensitive spots susceptible to sensation. When my Owner lays me on the bed, face up, and straddles me, She loves to flick my nipples with a fingernail. It’s much the same motion as kids use to shoot marbles on the playground (do kids still do that any more?). It makes the cock jump, and eventually drive it to orgasm. She will flick one, and i will beg Her to let me cum. “No,” She will say sternly — then flick the other one! Sometimes She will lean forward (my arms are immobilized) and tantalize me with Her own beautiful nipples: i must lick them ever so gently, until She grants permission to suck them softly. When She is ready (or has already had a climax or two!), She flicks both at once with a command, and my cock surrenders to Her delight. (Then, of course, She moves north and my tongue cleans Her while providing a few more for Her enjoyment.) She has not tried clips yet, but i have discovered what should be an excellent implement. Small wooden clothespins/pegs, only about an inch long, are just the right size to fit my smallish male nipples. Inexpensive at, of all places, a stationers. I have also seen them in gleaming metal on line for a lot more. Metal “crocodile” electrical clips look like they will tear the flesh, and they are quite strong. Perhaps a 3/16″ drill from side to side — forming a rounded hole in the toothy surface — would give a wicked appearance but not cut and bleed. Another possibility, based on an advertised custom item: medium-size cotter pis, spread with a sliding collar to tighten the tips. The “ring” at the end can be fitted with a Christmas-style “jingle bell” for added effect. Speaking of bells… at Christmastime, stores sell leatherette straps with half-a-dozen large 1″ bells and a ring on one end. These make excellent slave-collars! Feed the tip through the ring, along with one or two of the bells, and that’s all you need to do. Slave-bells, of course, let Mistress keep track of where Her slave is at all times, and the humiliation aspects go without saying.