(Oui, je sais bien!) It's a psychological term. I have no idea how it would translate properly en Francais...
One theory of perception and identification in humans is that one of the bases upon which we look at things and judge them is to see how it compares to each of the attributes that we identify with ourselves. Basically, how similar something is to us, and how different it is.
For example, we would generally see a dog, or a horse, rabbit etc. as different from us as they all have different bodies, different behaviors etc. whereas we'd see humans as being relatively similar to ourselves.
For things that we judge as being "different" and going from there, we derive pleasure from the similarities that we can spot. For example, we might find a dog yawning cute, because the dog is "different" to us, but yawning is a behavior that humans generally identify with strongly.
The "uncanny valley" is the place where something lies in the space where people are unsure whether it should be regarded as "same" or "other". One subject that commonly falls into this category are the 'anthropomorphs'- in this case I mean animals given a human structure, such as your mouse on the previous page (and therefore most of the things that I draw).
"Anthropomorphic" basically means "given the characteristics of a human"- obviously thus one can be "anthropomorphised" to different extents but the point remains the same- people tend to become uneasy at around this point.
Strangely, though, younger children are much more amenable to this same subject (think of the popularity of cartoon animal shows). I'd suggest this is because kids haven't formed the relevant identity constructs yet.
