Where All the kids were given sticks to keep with them whole night and with a threat that Thief's stick will grow by itself. So the thief cut his stick and in morning every one else has same size stick except the thief's stick was smallest....
so may be...Koki will say Who so ever has done the Swapping must have oil in her hand so the Impression of Fingers will tell the truth as some oil must be there on finger tips....and Rashi will dip her hands in Ghee (to save herself form Kagdi..đ) and on paper she will leave the Impression of Ghee......
Its May be or May not be the real picture that will come out tomorrow...but it was my first intuition after watching the epi...