Complete details of why the chicken crossed the road... ba dum bum
The question "Why did the chicken cross the road" is invalid. It is invalid because "why" assumes that the chicken had some reason for taking the action "cross the road". This, in turn, assumes that the chicken has the concept of "road"; after all, if the chicken doesn't know that the road is there, then the chicken did not - from the chickens point of view - cross the road, and consequently it is meaningless to ask for its motivations for doing so.
Since chicken is an animal, it is unlikely that it has the concept of road in the same sense than humans do; since it is a bird, whose ancestors were propably capable of flight in the near past, it is unlikely to have the concept of road in any sense - why would a flying bird need roads ?
Therefore, the chicken can never have any motivation for crossing the road, since from the chickens point of view, it never does any such thing. It simply moves from one point to another, and these points happen to be on the opposite side of a flat area of ground. No road-crossing has happened.
Think of it this way: if you walk over a scent trail left by some animal, and you don't know that the trail is there, it is foolish to ask your motives of crossing that trail. One can ask your motives for walking in the first place, but the crossing was pure coincidence and not something you chose.