Made a simple redstone pulse generator using the 'one torch, one repeater, 6 dust' design from the wiki, and surrounded it with a wooden fence. The pulser design was one that burns out if the repeater delay is shorter than 2. I set the delay to 4 and linked it to a dispenser and the setup worked fine for many game days. Then some chickens got trapped inside the circuitry, and I ignored them for some time, but after a while I found the pulser had burned out. I removed the torch and reset the repeater to a delay of 4 (but left the chickens there to see if they really were the culprits), and after a few days they seemed to manage it again?! Is it possible/intentional for a chicken to be able to bump a redstone repeater and change its setting?