The Crossed Out Words in YouTube Search Queries

Sometimes when you enter some words into the search box in YouTube to search videos, you will find that some of the keywords are crossed out, as the picture shown above.

YouTube doesn't elaborate why this happens. Below are some conclusions that I draw from analytics:

1. The crossed out words have no search result.
2. The crossed out words are not related to the search session.
3. The crossed out words are useless or needless which implies you that do not use those keywords in later search.

This feature is nice. But I don't think it's suitable for Google search, as it's almost impossible to find keywords that have no search result in Google search.