Natyashastra
वामपादेन वेधस्तु कर्तव्यो नृत्तयोक्तृभिः । द्वितालान्तरविष्कम्भो विक्षेपो दक्षिणस्य च ॥ ९१॥
The piercing with the left foot should be performed by the dancers. The space between the two Tālas is the extension of the right foot.
english translation
vAmapAdena vedhastu kartavyo nRttayoktRbhiH । dvitAlAntaraviSkambho vikSepo dakSiNasya ca ॥ 91॥
hk transliteration by Sanscript