Plot hole: During the previous episode, we find out that Dr. Bashir has been replaced by a changeling. But for the changeling's ruse to work, he would need to carry out all Bashir's duties. Which means he'd need all his medical knowledge. Bashir graduated second in his class at Starfleet Medical Academy. To learn all that Bashir knew would have taken longer than the Dominion and Federation knew about each other. Not only that, but to pull off all this changeling pulled off, he'd need intimate knowledge of Starfleet, Bajoran and Cardassian technologies. There's no way a changeling could have learned all that knowledge in the time alotted. Even if you use the excuse of the Great Link, the Founders would still need the time to amass the knowledge and at least one of them to learn all the medical techniques Bashir would have known to transfer that knowledge to the others, otherwise it would have been a dead giveaway Bashir wasn't really Bashir.