The tongue

One day, the master says to his servant:
Go and catch a pig, kill it and choose the best piece and bring it to me.
The servant obeys his master. He goes and kills the pig and bring the tongue to his master.
A few days after, the master, wants to put his servant's intelligence to the best, orders him to go and kill another pig and says that:
"Search for the worst part of the pig and give it to me".
After that, he offers again the tongue to his master.
The master asks him "How insolent you are! Why do you bring to me the tongue like the first time"?
The servant replies sedately:
"- Sir, there is nothing as good as the tongue when we are good, but when we wicked, there's nothing as bad as the tongue".