When Beta kills Gamma and props her up against a tree, Gamma is staring forward. After Beta kills the other Whisperer, the camera swings back to Gamma who is now staring off to her left.
To talk or even growl requires lungs expelling air into the larynx. Therefore, Alpha's decapitated head would not be able to growl as portrayed in the episode.
When Mary's nephew is passed to him, he is audibly crying loudly, but his face is shown and he is clearly not crying at all.