You are called to the table by West who tells you that South passed and now wants to change their bid.
South only has the 1D card on the table and tells you that they thought their partner bid 4S
You ask South, did you put the pass card on the table?
South replies no, and then demonstrates how they reached for the pass card then banged the table twice.
You ask South how they became aware that partner had bid 4nt and not 4S
South hessistates, West offers that North glared at their partner.
South offers no explanation.
How do you rule
