Rashi on Genesis 29:8/רש"י על בראשית כ״ט:ח׳

1לא נוכל WE CANNOT — give them water because the stone is a heavy one.

2וגללו AND THEY ROLL AWAY — This word is rendered in the Targum by ויגנדרון “and they will roll away” (whilst in Genesis 5:3 it is rendered by an Aramaic participle) because the verb has here a future meaning.