Read the passage and complete the sentence.
We use both words and gestures to express our feelings, but the problem is that words and gestures can be interpreted in different ways. A smile means the same thing in any language. So does laughter or crying. Animals show the same feeling too. For example, dogs, tigers and humans show their teeth when they are angry. Fear is another emotion shown in the same way all over the world. In Chinese and in English a phrase like «he went pale» suggests that the man is greatly afraid. However a phrase «he opened his eyes wide» suggests anger in Chinese whereas in English surprise. In Chinese surprise is described in a phrase like «they stretched out their tongues», which in its turn is very insulting in English. Disgust, contempt and suffering are the most different emotions for people everywhere either to recognise or to express.
According to the passage when animals are angry, they ... .