The mother-in-law comes home and finds her son-in-law furious and packing his suitcase.
"What happened?" she asked.
"What happened? - I'll tell you what happened!", he said, "I sent an email to Mary saying that I was coming home from my trip today. I got home and guess what I found?....... My wife, yes your daughter, with a naked guy in our marital bed! This is the end of our marriage, I will leave forever!"
"Calm down!" says mother-in-law, "There is something odd about this story. Mary would never do such a thing! Wait a minute while I check what happened."
Moments later she comes back with a big smile.
"You see, I told you there must be a simple explanation. Mary didn't receive your email!"