He could have made the same threat with his Ace hearts, as that would beat Karen's small talk of 5 spades, but it would have been easier for Karen to block. Unfortunately, Karen has the other 6 hearts and so blocks Richard and goes on to make a point in Hearts herself. The 5 hearts she plays is unbeatable as both 6's and the other 5 are already out. The sequence of cards drawn for each player was. Strategy hints The high and low cards are the key.
Aces whittle away at the opponent's hand size because they can force the opponent to change topic.
Only another ace or a card of the correct topic can be played on an ace. A pair of sixes can not be beaten, and guarantee that you'll make a point unless your opponent changes topic after your first play. Changing topic is painful because it reduces hand size and usually costs a card in the topic you want to make a point in.