Greg,

The following is on the web. A little looking suggests the text is drawn from Encyclopedia Brittanica. I can't vouch for the info, but it sounds reasonable enough.


"Cryptographic hieroglyphic writing
That knowledge of the hieroglyphic system and the principles upon which it was devised had not become lost is attested by two phenomena: cryptography and the development of the hieroglyphic writing during the last millennium of its existence. From the middle of the 3rd millennium but more frequently in the New Kingdom (from c. 1539 BC), hieroglyphic texts are encountered that have a very strange appearance. The absence of familiar word groups and the presence of many signs not found in the canon characterize these texts at first glance as cryptographic, or secret, writing. This kind of hieroglyphic writing was probably intended as an eyecatcher, to entice people to seek the pleasure of deciphering it. Composed according to the original principles of the script, these inscriptions differed only in that certain features excluded when the original canon was formulated were now exploited.
The new possibilities involved not only the forms of the signs but also their selection. For example, the mouth was not drawn in front view (), as in the classical script, but in profile (), although it had the same phonetic value. An example of a change in the choice of signs is the case in which a man carrying a basket on his head (), a deter minative without phonetic value in the classical script, was later to be read as f and was used in lieu of the familiar sign having this phonetic value, that of the horned viper. In the new selection of the sign, the phonetic value is obtained from the word f3 "to carry" (neglecting its two weak consonants), in accordance with a principle that the inventors of the writing had applied in 3000 BC. These cryptographic inscriptions prove that alongside the method of instruction in the schools, which was based on memorization or recognition, not upon analytical understanding, there was another tradition that transmitted knowledge of the basic principles of the hieroglyphic script. A command of the principles of hieroglyphics similar to that which the composers of the cryptic inscriptions had was presupposed for the puzzle-happy decipherers. Because the encoded texts often consisted of a petition by the inventor of the text to say a prayer on his behalf, the number of these decipherers must surely not have been small."

Lee


NOTE: I consider this a "fair use" of potentially copyrighted material for teaching/educational purposes only.