I just came across this intriguing video answer to that question.
First of all, I need to say that the presenter is slightly too inTENse in the WAy he spEaks. But don’t let this put you off, the content is interesting, cooky and sometimes plan daft, with many examples. Persist in viewing if you’re interested in words and wordplay. Or find yourself looking at a postcard and wondering how you can possibly write anything interesting in such a brief space.