witness and the substance of the testimony concerning which the expert witness is expected to testify, as soon as is practical, but in no event less than thirty (30) days prior to the beginning of trial except on leave of court. Tex.R. Civ. P. 166b(6). Rule 166b(6) does not address whether supplemental discovery responses must be verified. Nevertheless, there are several reasons why a party should be required to verify supplemental interrogatory answers despite the lack of an express requirement in Rule 166b(6). Rule 168’s command that “interrogatories shall be answered ... fully in writing under oath” applies to all interrogatory answers, initially and whenever supplemented. Tex.R. Civ. P. 168(5); see also Sharp v. Broadway Nat’l Bank, 784 S.W.2d 669, 671 (Tex.1990) (per curiam) (<HOLDING>). The rule does not distinguish between
holding that supplemental answers must be in writing as required by rule 1685 despite the lack of an explicit writing requirement in rule 166b6 holding that proof of an explicit agreement is not required recognizing rule holding district court need not make findings and conclusions as required by rule 52a because under rule 81a3 that requirement could be modified by issuing an order holding that the notice requirement found in rule 41d is not required by the fourth amendment