Be not forgetful to entertain strangers.

The hot dog vendor knits his brow, and a perfect cross appears - as if he'd come from from an Ash Wednesday service.  He relaxes into a grin; it disappears.  He concentrates on making change, and the cross is back: rectilinear, even, deep-shadowed, perfect.  It is as if one has entertained, or been handed extra mustard packs by, angels - unawares.