M. R. Evid. 614: Calling and interrogation of witnesses by court.

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

(b) Interrogation by court. The court may interrogate witnesses, whether called by itself or a party; provided, however, that in trials before a jury, the court's questioning must be cautiously guarded so as not to constitute express or implied comment.

(c) Objections. Objections to the calling of a witness by the court or to the interrogation by it may be made at the time or at the next available opportunity when the jury is not present.