Does anyone have any idea why one of my 10 week old chickens would be twitching its head frequently? It's the less active of the group, sits with its head somewhat into its neck, but not like a sick chicken does. She's quick to move if I approach, is eating and drinking well, walks and runs normally. I've lost two chicks of the same hatch last week, one I found in the run dead, no apparent reason, no sign of sickness earlier in the day and no sign of trauma. The 2nd one went down and just sat in one place for a few days, almost seemed like that one had Marek's, as the legs seemed weak, but for the rest the bird seemed healthy. It died after a few days. Now I'm watching them all, and see this one that has the twitchy head and is less active, but otherwise healthy. I'm feeding them grower mash and putting vitamins and apple cider vinegar in their water, give them clean water daily, put diatamaceous earth in their food in case they have worms, and DE in the shavings, in case they have lice or mites. I'm concerned about the twitch and decreased activity. Any thoughts?