MASHABLE - Feb 8 - According to this TED-Ed video, all five our senses play a role when it comes to physical attraction. Sight is the most obvious, though the perception of visual beauty can change dramatically once someone starts talking. More and more, however, attraction is being defined by the way someone makes us feel, and that is driven by how two people spark off each other. It can be that undefined reason why we instinctively flirt with one person and not another. According to eHarmony's study of ~1K Australian singles, the three ingredients for 'the spark' include: Easy flow of conversation, how much the person makes you laugh and how quickly you feel at ease around them. 50% of Australian singles expect sparks to fly by the end of the first date, and only 12% believe it's something that can develop over time. Long term happiness seems to blossom when there is more similarity.