I have 3 1/2 week old Cornish X and when I went to check on them this noon I noticed one standing on one leg and not running for the food like the others. He is holding one leg up in a curled up position. I didn't check him any closer because I didn't have time right then. What should I check for/do about this? I've kind of a chicken newbie so i've never seen this before and not sure how to procede. Thanks!