In Revelation 14:20, this signifies violence inflicted upon the Word by falsifications of truth. (Apocalypse Revealed 653)

653. And blood came out of the winepress, up to the horses' bridles. This symbolizes the violence done to the Word by the people's dreadful falsifications of truth, and the consequent understanding of it so closed up that it was scarcely possible for anyone any longer to be taught by it, and so to be led by the Lord through Divine truths.

Blood symbolizes violence done to the Word (no. 327) and the falsification and profanation of the Divine truth in the Word (no. 379). For blood from a winepress means the juice or wine produced from trampled clusters of grapes, and wine and new wine have the same symbolic meaning (no. 316). Horses' bridles symbolize the Word's truths by which the intellect is led, inasmuch as a horse symbolizes an understanding of the Word (no. 298). Thus a bridle symbolizes the truth by which that understanding or intellect is led. Up to the horses' bridles means even into the mouth into which the bridle's bit is inserted, and since a horse uses its mouth to drink and nourish itself, it also symbolically means that such violence was done to the Word by people's dreadful falsifications of truth that it was scarcely possible for anyone any longer to be taught by it, and so to be led by the Lord through Divine truths.

A bridle also symbolizes that by which the intellect is led in Isaiah 30:27-28; 37:29, and the blood of grapes symbolizes the Divine truth in the Word in Genesis 49:11 and Deuteronomy 32:14, though in an opposite sense in the latter case.