"As the bird by wandering, as the swallow by flying, so the curse causeless shall not come." (Prov. 26:2)
The American Standard Version gives this translation: "As the sparrow in her wandering, as the swallow in her flying, so the curse that is causeless alighteth not." The "swallow" referred to here is, according to Strong's Exhaustive Concordance of the Bible, a swift, a bird whose feet are not designed for landing on the ground. Their feet are more suited to clinging to rocks or masonry, and in fact swifts will not voluntarily settle on the ground.
This unusual imagery has a beautiful message for the deeper student of the Bible. It points to the fact that thoughts which seem to fly around in consciousness, but which bear a curse rather than a blessing, simply aren't equipped with the needed landing gear! They can't really become part of us or touch us in any way. Nor can they land in our mental territory when our thoughts are filled with spiritual truth.