[Kettle of fish]

Greatwarg,

Of course the greenway is covered in grass. It is just that the grass on any part that the chicken is not standing on (or that is in its very immediate proximity) seems greener.
The 'crossing' is possible as long as the chicken is on the edge, or just inside the edge, of the greenway.
Which brings us to the question of what would happen if we put the chicken on an endless greenway. Essentially, you would end up with a very happy chicken. The chicken would continue to walk towards the greener horizon and never reach it, therefore never finding out and suffereing the disappointment of its object being just as green as where it came from.
The next question to be addressed would be, if indeed the chicken would not eventually cotton on to the fact that it would never reach the horizon and suffer from sore feet which would lessen its happiness considerably.
And then of course, comes the question of whether chickens are colourblind.