How did Sai Baba prove to Cholkar that he knew about his secret vow involving sugar?

Sai Baba demonstrated his omniscience to Cholkar in a subtle yet profound way. As detailed in Chapter 15, Cholkar had privately vowed to abstain from sugar until he could visit Shirdi. After finally arriving and fulfilling his vow by distributing sugar, he went to stay with another devotee, Jog. As Cholkar was about to leave, Baba specifically instructed Jog to give him "cups of tea, well-filled with sugar." Since Baba himself did not drink tea, this instruction was clearly for Cholkar's benefit, showing him that his secret penance was known and his vow was accepted. This confirmation brought tears of joy to Cholkar's eyes and solidified his faith.