Kindly discuss and site example for Article 1561 of the Law on Sales. Thank you

Art. 1561. The vendor shall be responsible for warranty against the hidden defects which the thing sold may have, should they render it unfit for the use for which it is intended, or should they diminish its fitness for such use to such an extent that, had the vendee been aware thereof, he would not have acquired it or would have given a lower price for it; but said vendor shall not be answerable for patent