Head shaking

[Ezzfletcher]

One of my 5 week old chicks today has started to shake/flick its head from side to side and doing it quite a lot they have all been perfectly healthy they are all eating and drinking and pooping well etc they have are in the house but today I put them outside for an hour in their pen just for an hour wondered if that could be anything to do with it ... anyone got any suggestions?

 

[birdsrfun]

Did they have any access to grass? I’ve seen this when a chicken has a long blade of grass stuck in their throat. Are they getting grit?