While drinking milk that is very sour or chunky can result in food poisoning, milk that is starting to turn or is just after its expiry date is not likely to cause sickness. Children or those with weak immune systems are more at risk of food poisoning than healthy adults.
When milk is pasteurized most of its harmful bacteria is destroyed, but it still spoils rather quickly. Milk that is filmy or chunky or tastes or smells sour should be thrown away, even if the expiry date hasn't yet passed. If milk is left out for too long or the refrigerator isn't cold enough, milk spoils much faster.