Season 9: Episode 206: Tasteless Frank

Marie is astounded when Frank puts salt on her homemade lasagna, leading her to believe that she's lost her touch in the kitchen. However, Ray and Robert discover that the problem is Frank, who has lost his sense of taste. They believe it's a side-effect from some potency medication Frank is taking, but Frank doesn't want to give it up, and he doesn't want anyone to know he's taking it, especially Marie.