Bava Batra 152: Deathbed Changes to a Deathbed Will
When a person on his deathbed includes a formal act of acquisition in his gift under those circumstances, when that formal act is not required, given that he's on his deathbed, he's strengthening the commitment to the gift. Note that transfer of property via "shtar" - deed or document - only works while the person transferring property is alive. Also, the case of a deathbed will, and then a second one made too - the second will is the final authority. But does that make the first one "revocable"? It certainly brings us back to the dispute between Rav and Shmuel about the deathbed gifts.