Everyone loves to have fun with English. Studying sentences designed for native speakers of English can help ESL students who are preparing for an FCE or CAE exam. If you don't understand what's funny or strange about the expressions, ask me here in a comment, or ask another native speaker.
Since the Cambridge Exams seem to be examining students' knowledge of some idiosyncrasies of English as well as their general understanding and ability to use it, you might enjoy the following examples of language play. A post from buzzle.com lists more than 50 sentences that contain homonyms or pose questions about the irregularities of English. Very advanced level students might get the humor in the sentences in this very popular post at Writing English.