Wis. Stat. § 906.14: Calling and interrogation of witnesses by judge.

(1) Calling by judge. The judge may, on the judge’s own motion or at the suggestion of a party, call witnesses, and all parties are entitled to cross-examine witnesses thus called.

(2) Interrogation by judge. The judge may interrogate witnesses, whether called by the judge or by a party.

(3) Objections. Objections to the calling of witnesses by the judge or to interrogation by the judge may be made at the time or at the next available opportunity when the jury is not present.