My mother is 89 years old. She has been coughing mucus after eating. It is clear in color. She doesn t want to eat because it is embarrassing. She goes thru 10-15 paper towels trying to pull stringy mucus out of her mouth and throat. She has a history of a small esophagus which has been stretched in the past. She refuses to get another barium swallow test. She smoked for over 60 years and recently stopped. What could be causing the mucus.