Grog is rum and water, traditional drink of the Navy. Todays' useless fact although connected with music in a way..... When they brought Nelson's body back from Trafalgar, they put him in a barrel of rum to stop him 'going off', but didn't tell anyone. Sailors used to creep up to the rum barrel, slip a knife between the boards, twist and slurp up what trickled out.... hence the phrase 'a drop of Nelson's blood'.....

LTS

At least I think it was rum, it could have been brandy, but I'm pretty sure it was rum.