Caught in a lie

Alex and I are sitting on the sofa watching a video.  Suddenly, he let out a loud fart that actually vibrated the cushions of the couch.  I look at him and say "Alex!"  and he giggles.  A minute later, he does it again, a bigger sound that I thought possible to come out of his little butt.  "Did you fart again?" I asked him  "No."
"are you sure?"
"No"
"You farted."
"Daddy fahted" he lies.  Which normally would be a good lie because generally, if you smell something funny, it's John.  But unfortunately for Alex, John happens to be out of town today.  It's actually a shame, because these farts are the kind a father would be proud to have heard come from his son.  Chip off the old block indeed.