When reading super secret spy mail written in invisible ink, two properly functioning hands are practically a must. The better hand will be needed to operate the flame (a Bic lighter in this example) and the weaker hand can hold the note and move it around over the flame. I had no trouble reading the message, but nearly ignited the paper in a few spots. Have a fire extinguisher handy or alternately a partner to assist.
But then that creates another problem. You let someone read a For Your Eyes Only, so now you have to kill them.