Rimming, or oral stimulation of the anus, but there are a few precautions you should take before the fun begins. Did you know since the mouth comes into contact with the anus during rimming, it's possible to contract or spread parasites and STDs like hepatitis, some forms of which aren't curable?
Better to side with caution. So, no matter how clean your partner looks, use a barrier like a dental dam or cut and stretch a condom over the anus to avoid contact with your mouth or tongue.
Avoiding direct contact with the anus or anal fluids can help prevent the transmission of possible STD's like genital warts or HIV.