thorn
Explanation
This comic is about the Old English letter thorn (written as a character resembling "p" or "y"), which represented the "th" sound.
A character enthusiastically explains: "Did you know there used to be a letter 'thorn' in English? It looks like a 'y' but it's pronounced 'thorn' and makes a 'th' sound." Others respond with "Cool" and "Neat." The character continues: "It's used in a variety of languages — Old English, Old Icelandic, Old Norse..." and adds: "I enjoy studying these languages and the history of writing. Sometimes I make manuscripts using thorn and I like to share them."
Then someone asks: "Wait, are you getting at something?" The character replies: "You may have misunderstood when I texted saying you could see my homework, 'pornography.'" The final panel shows the horrified reaction: "NOOOOOOO."
The joke relies on the historical fact that the letter thorn was gradually replaced by the letter "y" in English, which is why old signs reading "Ye Olde Shoppe" were actually pronounced "The Old Shop" — the "Y" was a stand-in for thorn. The punchline reverses this: a word that appears to contain something scandalous ("pornography") actually contains the letter thorn, making it an innocent word (likely "thornography" — writing with thorn). The humor comes from the horrified misunderstanding by the recipient, who read the thorn as a "p" and got a very different message than intended.