Dr. calvin is giving a lecture on the properties of cardiac tissue. during the lecture, he states that the conduction tissue of the heart does not require any external stimulus to initiate its contractions. it has the ability to initiate its own electrical stimulation. to demonstrate this property, dr. calvin dissects a frog and places its heart in a petri dish with ringer's solution. he then asks his students to observe how the frog's heart continues to beat without any external stimulation. based on the information provided in this scenario, which property of the heart is dr. calvin trying to demonstrate?