There is, I understand, a species of modern poetry which is so written that it cannot be fully received unless all the possible senses of words are operative in the reader's mind. Whether there was any such poetry before the present century--whether all old poetry thus read is misread--are questions we need not discuss here. What seems to me certain is that in ordinary language the sense of a word is governed by the context and this sense normally excludes all others from the mind. When we see the notice 'Wines and Spirits' we do not think about angels, devils, ghosts and fairies--nor about the 'spirits' of the older medical theory. When someone speaks about the Stations of the Cross we do not think about railway stations nor about our station in life.
The proof of this is that the sudden intrusion of any irrelevant sense--in other words the voluntary or involuntary pun--is funny. It is funny because it is unexpected. There is a semantic explosion because the two meanings rush together from a great distance; one of them was not in our consciousness at all till that moment. If it had been, there would be no detonation. This comes out very clearly in those numerous stories which decorum forbids me to recall (in print); stories where some august person such as a headmistress or a bishop, on a platform, gravely uses a word in one sense, blissfully forgetful of some other and very unsuitable sense--producing a ludicrous indecency. It will usually be found that the audience, like the speaker, had till then quite forgotten it too. For the shouts of open, or the sibilations of suppressed, laughter do not usually begin at once but after several seconds. The obscene intruder, the uninvited semantic guest, has taken that time to come up from the depths where he lay asleep, off duty.
-C.S. Lewis, Studies in Words (Introduction), 1960
Link of the day: More puns at Worth1000 Visual Puns Contest