The excellent Welsh Bridge Union Swiss Pairs weekend in Llandudno in early July attracts a large entry from all over the UK. It is efficiently directed by Sarah Amos and the playing conditions at the Venue Cymru are good with plenty of attractions in Llandudno if there is time to enjoy them and lots of bed and breakfast accomodation available. The deal below is from this year's event.
After West's initial pass she then showed the majors by doubling one diamond, East showed some heart support and South jumped to three notrump hoping that there would be enough top tricks.
On an opening heart lead there were eleven top tricks and it looks as though the most likely way to generate a twelfth is to cash the top clubs and hope that the queen or jack falls singleton or doubleton. However, it costs nothing to cash lots of diamond tricks first to see what materialises. On the run of the diamonds both opponents discard hearts such that you expect West to have five and East four and, critically, West discards two small clubs. So you now know that East holds QJxx of clubs. After cashing all the major suit top cards the end position is as below.
Now a club to the nine endplays East to give you a twelfth trick. Making twelve was worth 72% as opposed to 36% for making eleven. One pair reached and made the excellent six diamonds and one pair bid and made six notrump.