(Devarim, Ibid.) "when He sees the hand going": when He sees one's strength waning in the exile, as in (Daniel 12:7) "and at the climax of the breaking of the hand (i.e., the strength) of the holy people," (the exile will come to an end).
Variantly: when they despair of salvation, when a perutah (small coin) "ends" from the pocket.
Variantly: "when He sees the hand going": when He sees that there is no one who implores mercy for them as Moses had done, viz. (Psalms 106:23) "He would have destroyed them had not Moses His chosen one stood in the breach before Him, etc."