Okla. Stat. tit. 22, § 22-320: Challenge to be made before jury is sworn - Exception

Neither the state, nor a person held to answer a charge for a

public offense, can take advantage of any objection to the panel or

to an individual grand juror unless it be by challenge, and before

the grand jury is sworn, except that after the grand jury is sworn,

and before the indictment is found, the court may, in its

discretion, upon a good cause shown, receive and allow a challenge.