I enjoy *The Walking Dead*, however one question keeps nagging me. The 'Walkers' are always shown to not have any intelligence or memory of having been human. This is for all seasons except the very first one.

In the very first scene of Season One, Episode One, we see a little zombie girl stop to deliberately pick up a teddy bear from the ground. 

Later in the same episode we see a zombie apparently try to turn the door knob to get into Morgen Jones' house.

Also at Atlanta they can climb fences and used rocks to break glass.

After season 1 I do not recall seeing any such intelligence demonstrated by a zombie again.

My question is: are these initial displays of intelligence a discrepancy in the story, or is there a plausible explanation why the Walkers performed these actions?