Grandpa's Murder


"Don't look surprised," said Grandma, "it's true I lost my hearing, 
but I can read lips, so ask me whatever you wish." 

"Well," said the detective, "I'd like to hear your account of your 
husband's death." 

"Well it was a breezy day and Grandpa and me went out on the lake 
for a sail.  When dusk arrived we anchored for the night. I was lying
in the cabin reading and Grandpa went to the deck for a smoke. You 
know, a few drinks, an unexpected wave and then, - over-board." 

Just then the grounds keeper started the lawn mower causing Grandma 
to shout that they better go inside. "As I was saying, being deaf I 
couldn't hear his cries for help." 

"You're lying said the detective."

How did he know?
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Answer:
If Grandma was as deaf as she claimed, she would have
not known to raise her voice above the sound of the
unseen lawn mower.