Arthashastra
शूलकूपम् अवपातनं वा शयन आसनस्य अधस्ताद् यन्त्र बद्ध तलम् एनं कील मोक्षणेन प्रवेशयेत् ॥
One may cause him to fall into a pit of stakes or a trap. Alternatively, by releasing the pins, he should be dropped through the bottom of a bed or a seat that has been mechanically fastened from below.
english translation
zUlakUpam avapAtanaM vA zayana Asanasya adhastAd yantra baddha talam enaM kIla mokSaNena pravezayet ॥
hk transliteration by Sanscript