An answer to (3): IMX, humans have a "stack"; we can understand deeply embedded sentences of the form "what did you bring that book I didn't want to be read to out of up for?", in contrast to the avians and mammals of my acquaintance, who seem to have a flat representation for utterances.
An answer to (3): IMX, humans have a "stack"; we can understand deeply embedded sentences of the form "what did you bring that book I didn't want to be read to out of up for?", in contrast to the avians and mammals of my acquaintance, who seem to have a flat representation for utterances.