Same goes for when we see someone repeatedly clenching their hands. Mental stress and physical tension are co-variant. They are also one of the most important muscle groups to keep relaxed. An increase in either typically increases the other. These wounds, even when they are microscopic , increase the chances of contracting sexually transmitted infections that can be transmitted orally under these conditions. An enema can also reduce the risk of direct fecal contact. It is believed that this is due to the transmission of HPV because this virus has been implicated in most cervical cancers. The only good times to clench our rear sphincter is 1 to hold in excrement, or 2 prevent something unwanted from entering.