A Smile.
What are you listening to that's making you so happy?
What's coming out of your headphones that's put a smile on your face?
An amusing podcast?
A humourous anecdote on the radio?
A song that's brought memories of a happy time back into your mind?
What is it that's put that grin on your face? It wasn't there before.
I would come and ask you, but I wouldn't want to interrupt the transmission.