Cascade, on Mar 2 2008, 03:53 PM, said:
The laws don't mention bridge reasons or anything like that as far as I am aware.
Law 73
D. Variations in Tempo or Manner
1. Inadvertent Variations
It is desirable, though not always required, for players to maintain steady tempo and unvarying manner. However, players should be particularly careful in positions in which variations may work to the benefit of their side. Otherwise, inadvertently to vary the tempo or manner in which a call or play is made does not in itself constitute a violation of propriety, but inferences from such variation may appropriately be drawn only by an opponent, and at his own risk.
2. Intentional Variations
A player may not attempt to mislead an opponent by means of remark or gesture, through the haste or hesitancy of a call or play (as in hesitating before playing a singleton), or by the manner in which the call or play is made.
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There is nothing that explicitly mentions 'bridge reasons'. What it does mention is that you can't hesitate or change the manner of play in order to fool the opponents. This is generally interpreted as 'if you didn't have a bridge reason for hesitating, you must have been doing it to fool the opponents'. Otherwise it would take a psychic to enforce this rule.