Columbo's ingenious line

There’s a great encounter at the airport after Leslie Williams (Lee Grant) takes Columbo for a flight in her small craft. The Lieutenant brings up an old friend named Ralph and Leslie curtly asks what the point was, to which the gumshoe responds: “…when you were talking about your husband in the plane, I guess that reminded me of Ralph. You see, because Ralph, he was a bore. I mean he was so perfect, there were times I felt like killing him.”

This was the definitive point where Leslie not only realizes the Lieutenant is on to her, but that he also knows her motive.