Two senses: (1) the involuntary 'tsk' click of disapproval; (2) the linguistic skill of trilling — the tongue-roll needed for Spanish/Russian/Italian R, which Mandarin itself does not use as a phoneme.
memory
弹 (tán) means 'to flick / pluck' (as in 弹钢琴 play piano) — picture flicking your tongue against the roof of your mouth.
