Laxative

The owner of this drug store walks in to find a guy leaning heavily against a wall. The owner asked the clerk: "What's with the guy over there by the wall?" The clerk responds: "Well, he came in here this morning to get something for his cough. I couldn't find the cough syrup, so I gave him an entire bottle of laxative." The owner, wide-eyed and excited, shouts; "You idiot! you can't treat a cough with a bottle of laxatives!" The clerk calmly responds: "Of course you can. Look at him. He's afraid to cough"