This is an old mariachi guitar technique to give the effect of a drummer joining the group!

Slap the fingertips (gently) on the uke body just below the strings. As you lift the fingers up, retract the index finger, strumming up across the strings at the same time. Follow this with a down up strum with the index. I’ll use ‘x’ to represent the slap, and ‘f’ for the finger up strum.

x f F f x f F f   F f x f F f x f
1 & 2 & 3 & 4 &   1 & 2 & 3 & 4 &

Note that the second version is just the same as the first, but with strums on the on beats and slaps on the off beats instead. If you have two uke players, one can do each, then you can fire the bongo drummer! (Just kidding!) You can vary this by alternating the slaps between just below the end of the fingerboard and just below the end of the bridge. Keep it comfortable – lifting the hand after the slap should automatically lead to the up strum.