The proprieties of bridge dictate that players should bid and play in even tempo and rhythm. An unusually long pause by a player before bidding or playing to a trick would be an undue hesitation. The player’s partner then has an obligation under the Laws to ignore any unauthorised information gained from such a hesitation.
You should take particular care not to hesitate and then pass as this conveys the information that you were thinking of taking a stronger action than passing. You should also avoid hesitating if you hold a singleton in the suit led or have some other forced play because it is against the rules to mislead your opposition by doing so.