A man and a woman who have never met before find themselves in the same 
sleeping carriage of a train. After the initial embarrassment, they both 
manage to get to sleep; the woman on the top bunk, the man on the lower. 
In the middle of the night the woman leans over and says, "I'm sorry to 
bother you but I'm awfully cold and I was wondering if you could possibly 
pass me another blanket." 

The man leans out and, with a glint in his eye, says, "I've got a better 
idea... let's pretend we're married." 

"Why not?" giggles the woman. 

"Good," he replies.  "Get your own blanket."