Danny Lavery welcomes Daniel Cohen, a Ph.D. chemical biologist working at a small biotech startup that is developing a new generation of antibiotics and anticancer drugs.  Lavery and Cohen take on three letters: First, from a letter writer whose laid-up roommate is barking demands. Another letter writer is wondering how to get started in getting involved in community issues. Plus, a check-in into the world of chemical biology.  Need advice? Send Danny a question here. Email: mood@slate.com

Production by Phil Surkis