When examined by an audio-expert, it was found that the echo was "swallowed" by the original quack, due to the very similar acoustic structure between the quack and the echo. Because of this, it may be difficult to tell where the quack ends and the echo begins. Normally, a sound and its own echo have very different waveforms on an oscilloscope. As it turns out, a duck's quack and its echo have a very similar waveform. Oscilloscope analysis of a duck's quack/echo could lead someone to mistake the echo waveform for part of the source waveform, due to the way in which they blend together. In the same way, human hearing may not perceive the difference between a duck's quack and its echo.