Highly unusual methods (HUMs) are bidding systems which turns the whole bidding mechanism over. Special defences are needed to deal with this kind of systems. They are classified as yellow sticker by WBF, and are forbidden in most of the events, except the highest level of events, in which they are subjected to a high level of restrictions. The definition of an HUM is a bidding system which exhibit one of the following characteristics: With the exception to the above being an opening of one of a minor in .