The formula itself uses the SEARCH function to find the position of “dog” in the text.
If “dog” exists, SEARCH will return a number that represents the position.
If “dog” doesn’t exist, SEARCH will return a #VALUE error.
We don’t care about the actual position, we only care if there is a position.
Case sensitive option
SEARCH is not case-sensitive.
SEARCH returns the position offind_textinsidewithin_textas a number.
When the text is not found, FIND returns a #VALUE error.