The story is allegedly true.  The scene is a Glasgow court and a witness (a ned) is being questioned by a rather plummy mouthed Advocate Depute (AD)

 
AD "You say you went to your friend house that night. Why did you go there?"
 
WITNESS "Tae get a tap."

AD "Is your friend a plumber?"
 
WITNESS "Naw."
 
AD "Are you a plumber?"
 
WITNESS "Naw."
 
The witness is a bit bewildered by this line of questioning and the AD realises it, but notices that the court police officer is rubbing his fingers of one hand together in the universal gesture of money.
 
Daylight apparently dawns on the AD and he changes his line of questioning accordingly.
 
AD "So you went to the house to borrow money?"
 
WITNESS "Naw."
 
AD "Ah. You went to the house to lend money?"
 
WITNESS "Naw."
 
In exasperation the AD says, "You told the court you went to your friend's house for a tap. What kind of a tap was it?"
.
.
.
.
.
.
.
.
.
.
WITNESS "A Sellick tap."