There's another scene in Swan Song that's not essential but makes me smile every time. When Columbo and Luke are standing by the table waiting for Tommy Brown to finish singing his song so they can talk to him, a little scene plays out like this:

Columbo looks at the food and says "This smells good."

Luke: "Help yourself."

Columbo: "Are you sure? I skipped breakfast this morning."

Luke: "It's fine. Help yourself."

Columbo lifts the lid and asks: "What's this?"

Luke: "Chili."

Columbo takes a bowl, takes a bite and says: "This is good, I've never had chili that tastes like this."

Luke: "That's a special recipe made out of squirrel meat. Dat's good ain't it?"

Columbo, putting the bowl down: "That explains it."

It's a short 30 second scene, not essential to the plot, but I smile every time I see it.