One of the more embarrassing, but not necessarily dangerous, effects of lactose intolerance is the onset of flatulence after eating dairy.  When the body does not have enough lactase to breakdown the lactose in the food, the undigested lactose sits in the gut and is broken down by bacteria.  The bacteria releases gases which in turn fill up the intestines and cause gas.  Depending on the amount of lactose, the individual, and the sensitivity of the person, symptoms could range from simple flatulence to cramps, diarrhea, or belching.