"Slide whichever circle is smaller entirely inside the bigger one, and now the answer is zero: You can’t draw any lines that touch each circle only once." This

"Slide whichever circle is smaller entirely inside the bigger one, and now the answer is zero: You can’t draw any lines that touch each circle only once." This sounds false. If the smaller circle is at the edge of the larger one, it is still entirely inside the larger one while a tangent line could touch both of them at the edge.