There's a sliding scale of what films get away with when using CGI to depict living creatures. If it's a fantastical monster of some kind, there's more leeway because nobody knows how such a creature would appear in the real world. When recreateing humans, however, you have a very high bar to clear - the audience will pick up on even the faintest whiff of fakeness.
Real-world animals are somewhere in between. Most of us aren't as familiar with monkeys or bears than say dogs, so filmmakers have a little bit of wiggle room. But when filmmakers are recreating something common like dogs or cats - much like people - they don't have much at all.
Because the integrity of many films rests in the realism of CGI, many people wonder why CGI animals are used in the first place. Maybe it was cheaper than using an actual animal - or more humane - or using a real animal would drastically increase filming time. Maybe the script called for the animal to do things animals don't normally do. Whatever the reason, the filmmakers pulled the CGI trigger, and now we get to judge them for it. Vote up the animals you can tell are completely digital.