When you play in real tournament sometime it happens to pull 2 cards, IF opponents dont call TD, they will accept you to play right cards, second card is an exposed card. In live tournament till we take the card we want to play , we pull it from other cards and put the card on the table ... pass few seconds. When we play on BBO we play from PC, tablet or IPhone is very easy to misclick. To click on the card you want to play take 1 sec and need to be very careful to check where the arrow of the mouse is. Each host can set the table, team match or tournament how she/he wish - with or without "undo". In 90% of the tournaments "undo" is not accepted(no undo), At table and in team match undo is set it in 90%. Is accepted because are playing between friends. Accepting an "undo" you cannot lose so much but you can make a new friend. "Undo" for misplay depend of each player. (i accept "undo" even for misplay).