One recent study looked at those expressions, and found that more often than not the new LEGO faces are angry. Here’s the basic setup of the study, from Research Digest: Bartneck obtained images ...

"but it appears likely to us that the dogs associate a smiling face with a positive meaning and an angry facial expression with a negative meaning." Müller and Huber report that the dogs were ...

In the research, dogs were trained to discriminate between a happy and an angry human expression from 15 pairs of photos which revealed only the upper half or lower half of the face. Researchers ...

But, he added, this did not show that dogs understood the meaning of those emotional expressions. Prof Huber agreed but added that the dogs that had had to touch the angry face to be rewarded ...

Once Müller and colleagues trained the dogs, they ran them through choice trials, in which the animals had to pick between strange faces with either happy or angry expressions. The researchers ...