hi! i just bought slap it from tony and its awesome, quite short but full off cool licks. but ive question to some of them. in some riffs there a are 2-note-chords with a T on it. Means ive to slap two strings simultaneously. but how does this work? ive got only one thumb and u only get a good slap sound with the joint and this way u only can slap one string. so how does he do that?