The salamander and the ermine, royal symbols.
These are just two examples. The first is a bas-relief above the castle's main entrance. On the left is the salamander, symbol of king François Ier, with a banner that includes his devise (motto), "Nutrisco et extinguo" (I nourish [the good] and extinguish [the bad]). On the right is the hermine (ermine or stoat), symbol of the queen, Claude de France. The ermine was the symbol of Bretagne (Brittany) and of Claude's mother, Anne de Bretagne, queen of France. Claude's father was king Louis XII. It looks like there's a banner above the animal with nothing written on it. I don't know if that's intentional or a partial restoration; it looks like some background elements are also missing.
A happy cherub.
The second sculpture looks to be a cherub that adorns the base of a ribbed vault in one of the castle's corridors. There are a lot of these around and whatever symbolic significance they have, beyond the purely decorative reflection of religious idolatry, I do not know.