Mary Lincoln's presence at Abraham's death-bed

[L Verge]

I sat beside my mother for two days and nights while she was dying from congestive heart failure and finally a stroke. I instinctively talked and sang to her most of the time. When the nurses found me doing that, they told me to keep going because the hearing is the last of the senses to be lost.

I can't know if my mother was brain-dead during this time because we have Do Not Resuscitate health instructions, but my question to Bill is whether or not Lincoln could have heard his wife after he became deathlike?