The third paragraph under the heading "Thresholding noisy data" (https://bioimagebook.github.io/chapters/2-processing/3-thresholding/thresholding.html#thresholding-noisy-data) recites:
... if we apply a Gaussian filter to smooth the image, a lot of the the random noise is reduced ...
The repetition of the word "the" is a typo.