Whether the animals are capable to smile or not remains controversial. Some scientists say that we tend to see human expression on the animal faces, but they do not exist. Meanwhile some studies take in consideration the possibility that animals could smile for real.
If you ask me I strongly believe that animals can show pain, fear, anger, love and happiness by gestures and facial expression.
Smiling baby urangutan
source: Nathan Roberton
source: BNPS Morgan Trimble