Sometimes it's the Small Things
It's been written that even the deaf can enjoy ILL, as Ball's facial expressions weren't just oversized or clownish; there was also great subtlety employed. Many of my favorite moments are the "little ones", or as they say in the industry, "throwaway business."
A couple come to mind.
In "The Million Dollar Idea", Lucy starts gulping the salad dressing at the close of her TV spot. Shortly afterwards, Freddie Filmore excitedly tells Lucy and Ethel that they've already started receiving offers. THIS is a plot point and the focus is on the this half-point in the episode. But all I'm laughing at is Lucy slapping her chest with indigestion. A tiny piece of business, but a big laugh.
In "Nursery School", Lucy "hides" Little Ricky to prevent him from being taken to preschool. When Ricky demands to know where he is, Lucy cracks her lips (the only way I can describe it) and says, "I'll never tell." A very funny bit that leads into several in this great scene.
Any others?