Theme 1-4 (aka Fortress House) is the 4th level in Angry Birds, and is the first to feature glass and blocks. It contains a single Small Pig that must be destroyed, who is inside a "fortress".
Three Star Strategy
Fire the first Red Bird straight into the fortress' left side. It should destroy the glass block, and move the wooden block. Fire the second Red Bird into the exact same place. It should hit the stone block, making it fall on the Small Pig. The player should then have two Red Birds left over, earning 20,000 extra points.