There is a moment in the 1985 sci-fi movie Cocoon that has haunted me for 25 years now. Senior citizens discover that the water in the pool they’ve been swimming in has a marvelously rejuvenating effect on them. Aliens have stashed the cocoon pods of their cohorts in the bottom of the pool of a rented house, awaiting return to the mother ship. These aliens are light-filled, radiant creatures who cover themselves in human skin to pass as one of us. The moment in the film that has stayed with me all this time is when the lead alien, played by Brian Dennehy, checks his human disguise in the mirror.…