T=thumb, S=slap, f=finger, h=heel, sh=shake
T S T sh (standard rhythm) T S T f/h/f (variation) T f/w S T T T S T S T S T sh
The samba rhythm forms a decay and then attack over the course of four beats. The analogy of a bouncing ball works: the initial impact is the first note, then a bounce for a second weaker impact then a third weaker impact. The fourth beat is strong again and slightly independent of the bouncing-ball analogy.
\ \ \ /\ \ \ / \ /\ \ \/ \/ \ \ 1 2 3 4 1 ... T f h S T f h S
The gap between notes is not regular, again like a bouncing ball the time between impacts is small after the first beat. Also the fourth beat is not delayed but races ahead. All told this gives the racing and syncopated feel rather than a regular metronomic beat.