Mo. Rev. Stat. § 490.490: When original shall be produced.

Where suit shall be brought upon any copy of a bond, or contract in writing, mentioned in sections 490.460 to 490.480 and the defendant shall, in his answer, or on motion to the court, deny the execution of such bond or contract, such answer or motion being verified by affidavit, the court may, if necessary to the attainment of justice, require the production of the original bond or other writing.