I have not had much time to watch the videos, so these are not extensive comments, but they should do.
Video 1
Up until the 25 seond mark, it sounds like you had just turned him on and he is doing the long hello sequence.
At the 40 second mark he is responding to the green colour just to his right, when he looks up the colour disappears.
After that he is responding to being on a tilted surface, and after a few more seconds freezes to prevent more battery loss/protection.
Video 2
Nothing interesting really to note in this video.
You keep touching him, so he never goes into explore mode. If Pleo keeps receiving touch sensor input, it won't go into explore mode, it will remain in social mode.
On a side note, his head servo does not sound healthy! (The one motor that operates the eyes and mouth)
Video 3
Nothing happens until 32 seconds.
At 32 seconds the Pleo starts to react to the green colour of the Daffodil stem.
At 40 seconds he stops reacting as he moves his camera out of view of the stem.
Hope this helps!
Degs