What does Genesis 44:14 mean?

With Benjamin essentially facing a life of slavery in Egypt for the theft of the Egyptian ruler's personal silver cup, all of Joseph's brothers return with him to Joseph's house (Genesis 44:7–12). Benjamin, however, is innocent. Joseph had his own steward place the cup in the boy's bag (Genesis 44:3–6). The eleven men don't realize the powerful man with whom they've been interacting is their own estranged brother (Genesis 42:7–8). These trials have been tests, of a sort, which Joseph has been using to see if they have changed since selling him into slavery twenty years ago (Genesis 37:24–28).

Joseph's brothers are desperate and heartbroken about what has happened. They find Joseph still at home. They throw themselves on the ground, prostrate (Genesis 37:7), as sign of respect and humility, hoping he will show them mercy.