two weeks ago 9 vaccinated chicks from mypetchicken arrived including this rhode island red that until today was behaving normally. all other chicks continue to act normally. today I noticed that this chick was keeping its head tucked down between its legs and walking backward only. mostly it backs into a corner and remains still, keeping its head tucked. some loud chirping but not incessant. it can raise its head but does not. I don't notice any other signs or symptoms. they all live in the basement in a chicken wire cage with a heating lamp. appear to be growing normally with organic feed and fresh water. have quarantined with available food and water. can't seem to find any answers on the web. any ideas what is wrong with this chick? appreciate any help.