4 KudoZ points awarded for this answer. Comment: "Thanks to you all and a Happy New Year to you all! When we say there is chemistry between a male and female, they are not yet “有染”I guess; they might be “有染”when some "chemical reaction" happens:-) “投缘”and “默契”are both good, but seem not as powerful as "chemistry". Mr.Fu's “来电” accurately catches the starting moment of "chemistry", since when they have chemistry, they "turn on" each other immediately when they are together. Therefore, it seems to me "chemistry" embraces both “来电”and “默契（投缘）”, If we have to make a choice, “来电”should be the second best next to the original for the time being. Bill"