The mother-in-law arrives home from the shops to find her son-in-law Paddy in a steaming rage and hurriedly packing his suitcase.
"What happened Paddy?" she asks anxiously.
"What happened? I'll tell you what happened. I sent an email to me wife telling her I was coming home today from my golfing trip. I get home... and guess what I found? Yes, your daughter, my wife Jean, naked with Joe Murphy in our marital bed! This is unforgivable, the end of our marriage. I'm done. I am leaving forever!
"Ah, now, calm down, calm down, Paddy!" says his mother-in-law. "There is something very odd going on here. Jean would never do such a thing! There must be a simple explanation. I'll go speak to her immediately and find out what happened."
Moments later, the mother-in-law comes back with a big smile.
"Paddy, I told you there must be a simple explanation... she never got your email."