929 NIN Riddle (Just For Fun)

A Riddle a day keeps the doctor away...  See if you can figure our riddle out...

Romeo and Juliet are found dead on the floor in a bedroom. When they were discovered, there were pieces of glass and some water on the floor. The only furniture in the room is a shelf and a bed. The house in is a remote location, away from everything except for the nearby railway track. What caused the death of Romeo and Juliet?