A diary entry belonging to a senior member of the Secret Intelligence Service (MI6) has revealed that during the First World War it was discovered that spunk could act as an effective invisible ink.
In June 1915, Walter Kirke, deputy head of military intelligence at GHQ France, wrote in his diary that he "heard from C that the best invisible ink is spunk", which did not react to the main methods of detection. Furthermore it had the advantage of being readily available.
"007", she said.
"Yes, Ma'am", he replied, his intelligent eyes piercing the half gloom.
"Come over here and have a wank in this jar", commanded 'M', her eyes, twinkling in anticipation.
Doesn't have the right ring to it, does it?