Law 45C4b
The law says "A change of designation may be allowed after a slip of the tongue, but not after a loss of concentration or a reconsideration of action."
What does a slip of the tongue look like, and how do we distinguish between that and loss of concentration?
Declare calls for a spade "spade please", then when dummy plays a low one says "no I meant the ten". Is this a slip of the tongue or a loss of concentration?
I ask because I'm not sure they exist.

Comments
Well, the example from when I took the TD course that Phil Godfrey likes to relate is of a player saying small club while quite clearly pointing at diamonds and saying "no, small club" when a club is selected, animatedly pointing at the same suit. They're quite obviously not intending to play a club.
And I do sometimes find my brain supplies the wrong card, but I don't see how the TD is supposed to know this and prefer to just keep playing. When you say spade and then correct yourself it always seems like a loss of concentration to me.
I use exactly the same simulation as James and Phil Godfrey!
Barrie Partridge - CTD for Bridge Club Live
They certainly exist, but may be hard to tell. An obvious way in which they exist is when people are using a second (third?) language and get the word muddled.
I generally find that if the distiction is clearly enough explained to players, they know (and accept) if it really was unintended within the meaning of the law.