User blog comment:ImperiexSeed/Are fairies really capable of snekaing into Lucifer's Cage? If so, how?!/@comment-1509826-20120103193956/@comment-3481504-20120103203154

Even still, it's generally excepted that breaking into the Cage is impossible, thus it had to have been a bluff. However, Castiel was able to, with great effort, enter the Cage.