Marital research

Isaac has been quietly perusing a document for some time and his wife Rose
is getting curious. So she asks him, "Nu, so what are you reading, Isaac?"
"Our ketubah," he replies.
"But you've been staring at it now for nearly an hour," she says.
"I know," Isaac replies. "I'm looking for something."
"So what are you looking for, Isaac?" asks Rose.
"An expiry date," he replies.