I've always thought that you should slip with the same snap and violence that you use when throwing punches. The motions are the same and you should always counter when you slip. Examples: Slipping inside a left jab (so it goes overyour right shoulder) is the exact same movement as throwing a straight right hand. Slipping outside a right hand and countering with a right, same move. Slipping outside a jab and throwing a left hook are the same move.