A story more than 12 years old.
Maybe not a real Grosvenor, but at least it contains a forum member cheating.
My partner and I played in a strong club vs a famous/infamous pair, who played (very) HUM. On one hand my partner was declarer in 3NT with 432 in hearts facing 65 in the dummy. The opponents took ages to cash their four heart tricks, including a few technical unblocks. During the play my partner studied their system-declaration intensely, trying to get a generel overwiew of the opponents system.
After the hand a longer discussion ensued, as to whether it was unethical of my partner to study the declaration, with the aforementioned heart holding. I went to the bar for refreshments, not really expecting tempers to have cooled down when I returned.
Next hand I was declarer (spotcards inacurate):
Going through invitational sequence we ended in 4
♠ declared by South, and doubled by RHO.
The defence started with two rounds of clubs, ruffed by South.
I was at crossroads. With thrumphs 3-2 It would be simple to draw two rounds of thrumphs, then knock out the ace of hearts. However that could backfire the -800/-1100 way, if thrumphs were 4-1. And I wasn't in the mood for another of those.
I decided to play a round of hearts first, risking a ruff if they were 5-1. I led a low heart towards dummys KJ3, and LHO made what was known as "the top player fidge", just enough to make declarer believe he had something to consider, but not enough to get any TD to rule against him.
"Relieved" (I made quite a show) I asked for the King.
It was taken by the Ace. I could now safely draw two rounds of spades. As they were 3-2, the contract rolled home.