“They broke entirely new ground, Helena. No one had recorded anything quite like them before.”
“They provided the missing ingredient,” Mayo agreed. “In them, nature had taken the one vital step forward and had provided us with the concrete physical phenomenon which made their communication capable of test. Willie had two birthmarks. It sounds damn silly, but there they were. They were pale-pink patches, one inside his left wrist and one beside his left eye. In the normal way there was nothing unusual about them and they weren’t very noticeable, but when Len Drummond sent his brother a message of warning—when he released an unfriendly impulse toward him—the birthmarks changed color and became deep livid bruises. Anyone could see them and they could be recorded. So you see it did not matter
