James 3

"With the tongue we praise our Lord and Father, and with it we curse human beings, who have been made in God’s likeness.  Out of the same mouth come praise and cursing. My brothers and sisters, this should not be.  Can both fresh water and salt water flow from the same spring?  My brothers and sisters, can a fig tree bear olives, or a grapevine bear figs? Neither can a salt spring produce fresh water." vv.9-12

Read chapter 3
The tongue.  Crazy the power it has for such a small part of our body.  Power that can be good and bad.  Yet the tongue is the one beast that man cannot tame.  I mean man has been able to tame the most furious of beasts but the tongue is that much more ferocious. It's also hypcritical: speaking cursing and praises to God.  We see the dumb down comparison in nature.  Salt and sweet water don't come from the same spring source, a fig tree doesn't bear olives, a grapevine doesn't bear figs.  Nature teaches us that opposites aren't produced by the same thing so neither should our tongue.  Yet God can make something bitter sweet as we see in Exodus 15:22-25

So Moses brought Israel from the Red Sea; then they went out into the Wilderness of Shur. And they went three days in the wilderness and found no water.  Now when they came to Marah, they could not drink the waters of Marah, for they were bitter. Therefore the name of it was called Marah. And the people complained against Moses, saying, “What shall we drink?” So he cried out to the Lord, and the Lord showed him a tree. When he cast it into the waters, the waters were made sweet. 

Only the work of God can make something go against nature, and only the Holy Spirit in us can tame our tongue if we choose.
The childhood song "Sticks and stones may break my bones but words will never hurt me" is a false statement, or at least one that is an encouraging statement to strive for, as words can hurt longer than any physical pain.  The tongue can bring comfort and encouragement or it can bring hurt and destruction.  We have to choose how we're going to control our own tongue.  Like in the chapter one we should be "quick to listen, slow to speak and slow to become angry."