The old gameshow To Tell The Truth... a panel of minor celebrities ask 20 yes/no questions to three people presented as being a given minor celeb of note whom 99.9% of people just don't know what looks like..
The host introduces the panel and then says ... Now lets play... To Tell The Truth! *curtain parts*
3 female figures stand in shadow. A spotlight hits the first one... she stands forward and says: My name is Hellen Keller...
Spotlight moves to woman 2... she stands forward and says: My name is Hellen Keller...
Spotlight moves to woman 3... she stands forward and says: MWWHHyhyy nnnaAAhhhhhaMMeeee eEEEeesss Hewwwwwen KKwewweellllleerrrrr....
its an era based joke. Anyone over 30 in the states was raised upon a steady diet of Hellen Keller jokes.. I guess it something that had to be imprinted in childhood. We laugh because it helps trigger old memories of 100 old dusty jokes deep in the brain database. We remember them all in a little way all at once.