Manners expert Helena Echlin from Chow.com recommends being direct but discrete. Wait a few moments to see if the person catches it themselves, and then quietly draw their attention to the problem.
You can try communicating nonverbally by catching their eye and tapping your teeth (or touching your face to show where the errant piece of food has landed). If that doesn't work, a brief whispered message does the trick.
We also feel it's best to pass on the message and then carry on as if nothing happened. Start a conversation with your other dining companions to give the person a few moments to take care of things. Or if it's just the two of you, look away and then pick up where the conversation left off.
Most of the time, the person will be embarrassed but grateful for your intervention. After a few moments, the awkwardness inevitably fades and the night moves on.
How do you handle this situation?
• Read Helena Echlin's full article, "Is There Something in My Teeth?", on Chow.com
Related: Do You Share Food?