After spending some more time yesterday browsing for a new laptop, I came back to the office and plugged some speakers into my Mac so that I could listen to music while filling in forms for ethics review. At the end of the day I pulled the RCA jack out of my computer, folded it up, and biked home. When I opened up my Mac in the evening, the sound wasn't working: the volume control still showed up on the menu bar, but the slider was frozen in the "max" position. System Preferences > Sound > Output tells me I only have one output device (Name: "Digital Out", Port: "Built-In Output"), and says, "The selected device has no output controls". Volume can't be adjusted there, either --- the control at the bottom is grayed out with the slider in the "max" position. The only thing that seems different from normal is a small red LED inside the RCA port for the audio output, but as I watch, it switches itself off. Reboot. The Mac going "bong!", so the internal speakers are still working. Still no sound once OS X is up and running, though. Plug in speakers: yup, they work (the volume control comes back to life on both the menu bar and System Preferences). Unplug the speakers: volume controls grayed out, no sound. On to Google. Several people reported this problem between 2006 and 2008; for some, it just went away on its own after a reboot, but others were still plaintively asking, "Can anyone help me?" three months after their initial post. Looks like I'm heading to the Apple Store at the Eaton Centre this morning... My real question, though, is, "How did it know?" How did my Mac know my thoughts are straying? How did it know that I'm planning to replace it? I don't follow Slashdot or other tech news channels the way I used to, but I'm pretty sure I would have seen an announcement about iTelepathy being released... Update: turns out there's a wee switch inside the Audio Out port that's supposed to detect what kind of jack you're using, and it jammed in the "optical" position when I last unplugged the speakers. Thanks to Jason M., it's now unjammed, and I have audio once again.