"It is desirable, though not always required, for players to maintain steady tempo and unvarying manner. However, players should be particularly careful when variations could work to the benefit of their side. Otherwise, unintentionally to vary the tempo or manner in which a call or play is made is not an infraction. Inferences from such variations are authorized only to the opponents, who may act on the information at their own risk."
In other words, it is not unlawful for a player to stop to reevaluate and think before he calls or plays, but is unlawful for partner to decide his action based on partner's tempo or manner. Another instance of unauthorized information.
"It is unlawful for a player to attempt to mislead the opponents by means of a question, remark or gesture, by the haste or hesitancy of a call or play or by the manner in which a call or play is made."
In other words, a player who hesitates before he plays in an attempt to disguise a singleton or to imply that he has a missing honor when he does not is a serious offense. You will be penalized, suspended and made to display a scarlet letter C on your chest.