Mass. Gen. Laws ch. 185, § 41: Answer

Section 41. Any person who claims an interest, whether named in the notice or not, may appear and file an answer on or before the return day, or within such further time as the court may allow. The answer shall state all objections to the complaint, shall set forth the interest claimed by the person who files it, and shall be signed and sworn to by him or by a person in his behalf.