Both the reading and the lecture talk about the possible sources of the sound “quackers”, which were detected by Russian submarines during the 1960s to 1980s. The author of the article points out three theories. However, the lecturer disagrees with all of these hypotheses, saying they are not convincing enough.

To begin with, the author suggests that the sounds may be made by orca whales during a courtship ritual. It is said that orca whales' habitat matches the place where the sounds occur and they can make very similar voices. The lecturer argues that orca whales usually live near the surface of the ocean, so the sound made by them is impossible to penetrate the deep ocean where submarines are. Besides, orca whales are easy to detect by sonar.

Secondly, the author contends that the sound maker may be the giant squid. He backs this theory up with the statement which indicates that giant squid is hard to be detected due to their soft bodies and they emit sound because of curiosity. The lecturer posits that if the sounds were made by giant squids, they should continue to occur until now because they are living there all the time. However, these sounds only lasted for two decades and stopped suddenly.

Finally, the author asserts that another country’s submarines with advanced technology are the source of the quackers. The lecturer casts her doubts on it by bringing up the fact that an object as giant as a submarine can not change direction rapidly and submarines run always accompanied by engine noise. These features oppose the detective results of the sounds. She adds that even today, we can not build a submarine that is fast and silent like this.