The meaning of, 'Oh, Watson, the needle!'
Sherlock Holmes was satirized in English music hall skits, in which the line, "Quick, Watson the needle," was noted. This bit found its way into American vaudeville skits in which Holmes appeared. The line, or variations thereof, became familiar on both sides of the pond. Apparently, Rathbone as Holmes is making a little homage to this quaint tradition.
"Ignore the man behind the curtain!"