Leopards can't change their spots by Foxymoron

This expression basically means that things cannot change their innate nature and the first reference to it that I could find is in the Geneva Bible, 1560:

"Can the blacke More change his skin? or the leopard his spottes"

However, researchers at Bristol University have shown that leopards do change their spots depending on their surroundings, and will tend to blend in to their habitat. Black leopards are not found in open savannah.

In bridge the expression is often used about a second double being just as much takeout as the first double. But there has to come a point when it changes to a penalty double and this interesting hand from tonight's duplicate was such a position.

East opened a multi at this table, and South had to start with a double. West's 4D asked partner to bid her major, which turned out to be spades, surprisingly. South doubled again, which is not penalties but more takeout and I might bid 4NT as North now, two or more places to play. One North passed and he was soon writing down -790. 5D worked ok, however, although now West will get a club ruff but that would still make. West went on to 5S, of course, and now the final double by South has changed its spots and is more penalty-orientated. South led the king of hearts, a good choice, as that asked for count, and North played the eight of hearts, showing an even number. Now there is no hurry to cash a second heart - it is clearly not going anywhere, and South should cash the ace of diamonds, on which North will play the jack if playing normal attitude or the five if not. Then a second diamond defeats the contract. As making 4S for EW was an average (even though South can make 6D) any plus score for NS is very good. Poor Vampyr (Stefanie Rohan), and her partner Ken Rolfe, had to judge very well to sacrifice in 6Sx-2 for 5% of the matchpoints. Sometimes the field is just not on your side.