A guy n his mistress went to a clinic and asked the doc to observe their sex and see if they were doing correctly.The doc obliged and charged the couple $20

The next day, they came again, the doc charged $20.

Finally, after so many visits, the doc, puzzled, asked why they came to him.

The guy said, "if i were to get a hotel room, it would cost $30 and if i went to either her house or my house, my wife, and her husband would whack me."

"When i come to u, however, i get charged less and can claim $30 from my medisave account."