The first to seize the other's lip is the winner. As in a game, it is necessary to take the other by surprise. Since there is a winner, a quarrel is inevitable, which is also a stimulant.
english translation
चुम्बनद्यूत का लक्षण नायक-नायिका में जो पहले दूसरे का अधर चूम ले, वही जीतेगा ॥ १४ ॥