When Is It Time To Say Goodbye? Imagine you’re having a conversation with someone. You may get the sense that they have somewhere else to be. Or you might start feeling restless, and use an excuse to cut the conversation short. Sometimes, you feel like you could talk for HOURS. Chances are you’re wrong every time.  In a study published this week in the Proceedings of the National Academy of Sciences, Adam Mastroianni and colleagues tried to figure out how good humans are at judging the ideal length of a conversation. They found that both participants agreed a conversation ended at the right time in only 2% of their trials. And the difference between one partner’s desired conversation length and the actual length of a conversation could be as much as 50%—so in a 10 minute conversation, your partner might have wanted to talk to you for as little as 5 minutes, or as much as 15 minutes. SciFri’s Charles Bergquist talks with Mastroianni about these results, and why the “exit ramps” to a conversation are rarely where you want them to be. Talking Through The History Of Our Teeth Most of us have never thought much about why we have teeth. But if you’re the parent of a teething infant, the question becomes a whole lot more relevant: While you impatiently wait for baby’s teeth to poke through, or soothe your teething toddler in the middle of the night, you might find yourself wondering why humans go through all this trouble for a set of teeth that are only temporary. In a decade, your child will have shed their baby teeth to make room for their adult counterparts, and all this fuss will be but a distant—albeit painful—memory for both you and your former infant. But one such question can lead to another. Are baby and adult teeth made of the same stuff? Why can’t we just grow a new tooth if we lose one? And how did ancient people take care of their teeth? Biological anthropologist and ancient tooth expert Shara Bailey joins Ira to discuss why our teeth are the way they are.  A Look Back At The Time Of The Tasmanian Tiger Last week, conservation biologists on Twitter were all aflutter as rumors circulated that a creature called a “thylacine,” better known as a “Tasmanian tiger,” had been caught on camera in the Tasmanian bush. Thylacines have been considered extinct since the mid 80’s, but there are still those who believe—or hope—they still exist.  In a video posted to YouTube, Neil Waters, President of the Thylacine Awareness Group of Australia, shared the news of what he thought looked like images of two adult thylacines and a baby. Unfortunately, this time the animal caught on camera was identified as a pademelon. But at Science Friday, we’ll never pass up an opportunity to celebrate a charismatic creature. Last January, SciFri’s Elah Feder spoke with Neil Waters and Gregory Berns, a psychology professor at Emory University, about the fascinating history of the Tasmanian tiger.