A party examined by an adverse party may be examined on his or her own behalf, in respect to any matter pertinent to the issue. But if he or she testify to any new matter, not responsive to the inquiries put to him or her by the adverse party, or necessary to qualify or explain his or her answer thereto, or to discharge, when his or her answer would charge himself or herself, such adverse party may offer himself or herself as a witness, and he or she shall be so received.