Parties retaining multiple declarants in connection with a post-issuance trial before the Patent Trial and Appeal Board (“PTAB”) should review a recent decision by the PTAB relating to discovery into communications between two declarants. During the depositions of Patent Owner’s declarants in Apple Inc. v. Achates Reference Publishing, Inc., IPR2013-00080, Paper 66, (Jan. 31, 2014) and Apple Inc. v. Achates Reference Publishing, Inc., IPR2013-00081, Paper 58 (Jan. 31, 2014) both declarants testified that they discussed certain prior art references by email while they were preparing their declarations. Petitioner sought discovery of those emails exchanged between the declarants. The Board concluded that “Petitioner cites portions of the depositions of [the two experts] where the witnesses testified that they had direct email communications with each other regarding the prior art at issue in these proceedings.” The testimony showed that they used each other as “sounding boards.” The Board explained that the deposition testimony of the witnesses “indicates that they exchanged emails regarding the challenged patents and prior art, and at least considered the statements in those emails (in addition to the other individual’s declaration) in forming their opinions regarding the alleged patentability of the challenged claims over that prior art. This testimony indicates more than a mere possibility or mere speculation that something useful will be uncovered by producing the emails. Petitioner’s request is otherwise proper as well, as it is narrowly tailored to a small number of emails that would not be overly burdensome for Patent Owner to answer.” Thus, while the standards for obtaining discovery in IPR are rigorous, and the PTAB has not been granting discovery very often, parties may expect that communications between witnesses related to the subject matter of their testimony will likely be discoverable. Therefore, Petitioners should ask questions during deposition to unearth any such discussions if their opponent has retained multiple experts, and counsel for parties using multiple witnesses should carefully monitor their communications.