Really likes his scratches

My cat does something odd that someone here might be able to explain.
When I scratch him on the back near his tail, he will in short order tilt his
head to one side, cock his chin up a bit, then start seemingly lapping the air
with his tongue.
Now, I'm cool with this so long as it's just a pure pleasure thing. But if
Goliath is getting something kinky out of it, I may have to flick that boy up
side the head. Anyone else have a cat do this, or know of it?
Ken