When you buy fresh vegetables like cauliflower, broccoli, lettuce etc. little bugs may be hiding inside the leaves and the florets, and it is hard to get rid of them.
The best way is to make them come out of their hiding places is to immerse the vegetables in a bowl of water where you have added a handful of salt or half a cup of vinegar. Leave them for ten to fifteen minutes and then rinse them with plenty of clean water. Your veggies will be totally bug free!