It’s time again for our listener mail round-up, and this week, the theme is borders and boundaries. We learn what it means to define the “end of an era,” explore how close is too close to a black hole, and discuss the power of animal urine. Plus, we hear the story about the time the U.S. and Great Britain almost fought a border war… because of a pig. How do different animals mark their territory?How does surveying work?How close do you have to be to get pulled in by a black hole?How do historians decide how to categorize chunks of time?Featuring Eric Salovich, Naoufal Souitat, Dagomar Degroot, and Christine Wilkinson. SUPPORTOutside/In is made possible with listener support. Click here to become a sustaining member of Outside/In. Talk to us! Follow Outside/In on Instagram or Twitter, or discuss the show in our private listener group on Facebook. Submit a question to our Outside/Inbox. We answer queries about the natural world, climate change, sustainability, and human evolution. You can send a voice memo to outsidein@nhpr.org or leave a message on our hotline, 1-844-GO-OTTER (844-466-8837). CREDITSHost: Nate HegyiReported and produced by Nate Hegyi, Taylor Quimby, Justine Paradis, Felix Poon and Jeongyoon Han. Edited by Taylor QuimbyExecutive Producer: Rebecca Lavoie Music by Blue Dot Sessions.Outside/In is a production of New Hampshire Public Radio