The "possibility" referred to in line 6 is a possibility that the pigeons could read the minds of the experimenters. How could we test if this is true? One way to do it would be to use handlers that are unaware of the location of the pigeons home as (A) states, in that case if a pigeon is usually able to find his home by reading the handler's mind, the pigeon would be lost, but if a pigeon is still able to "home," there must be an alternative explanation.
