Given scene/plot descriptions from movies or TV shows, and given a specific question about the scene, summarize the question into a title

At the end of Stranger Things' second season, we see that    Will uses Morse code to secretly communicate with Hopper while the monster is possessing him.  Why does Will know Morse code? Did I miss something? Hopper and Eleven know it, Hopper due to his military training, Eleven due to being taught, but Will just doesn't seem to have any particular reason to do so.
Why does Will know Morse code?

In Interstellar, after Cooper arrives in the Tesseract, Cooper tries to send the message STAY to his daughter in the past so she won't let him go on the mission. If that was his intention then why did he send the coordinates of NASA afterwards? If he didn't send the coordinates, he wouldn't have found NASA or go into space, he would have stayed.
If Cooper wanted to stay, why did he send the NASA Coordinates?

In the 2004 film, The Village, the villagers wear yellow as a "safe" color to protect themselves against the creatures that live in the woods beyond the borders of their village. The color yellow is to show the creatures that the villagers mean them no harm and that peace is to be maintained between them.  Ivy Walker (who is blind) needs to breach the borders and go into the woods. It is revealed to her by her father that the creatures actually do not exist, but they were simply used as a scare tactic to prevent the villagers from venturing into the woods and going to "the towns."  Ivy still wears her yellow cloak. She falls into a hole and gets her yellow cloak covered with mud. Realizing that something is following her, she gets extremely nervous and frantically tries to wipe the mud off of her cloak to reveal that she is wearing yellow.    If Ivy knew that the creatures were not real, why was she trying to reveal the color of her cloak?

Why was Ivy concerned with wiping the mud off of her yellow cloak?

