User blog comment:Monkey.D.Me/SOUL FAQ (*^*)/@comment-3075024-20120301131223/@comment-4493594-20120301132128

Nutri-what-now? Whether they can sense him or not depends on how people are sensed by haki and whether it makes a difference if he has a body or not. Maybe he doesn't have enough "presence" as a soul to be sensed but we cannot say that for sure.

Soul Mode Brook getting a blast of Haki in his spectral face:
 * Nothing happens because he's a soul
 * Gets blasted back into his body
 * He dissolves and recomposes himself again severly weakened
 * His ghostly ass gets sweeped straight back to yomi