There is a member of INGO on the north side of the river and a member of KYGO on the south side. They want to get together. INGO tells KYGO to swim over. KYGO can't swim. INGO says "I'll shine my flashlight across the river and you walk across on the beam."
KYGO says "I ain't that smart but I know better than that. You'll shut the light off when I get halfway over!"