Container Egg for Secret Messages

Giambattista della Porta s Magiae Naturalis (1558; 1644 ed. Book 16Chapter IV) and Thomas Luptons A Thousand Notable Things (1579) give a step by step description how to secrete letters in eggs: To put a Shedule, or lytle wryting into an Egge, lay an Egge certaine dayes in strong vynegar, vntyl it be soft, and wryte your name or what you lyst in a lytle peece of paper, and folde the paper as harde together as you can: then with a Raser cut the sayd Egge in the toppe fynely, and aduisedly: through the