Carl Gallups chooses to start explaining the third trumpet, as this was the prophecy that made him realise that we are indeed living in the days of the trumpets. You can read the biblical text for the third trumpet below (Revelation 8:10-11).
Third Trumpet: The Waters Struck
“Then the third angel sounded: And a great star fell from heaven, burning like a torch, and it fell on a third of the rivers and on the springs of water. The name of the star is Wormwood. A third of the waters became wormwood, and many men died from the water, because it was made bitter.