VideoMentions scrapes the video page markup and pulls out the "baseUrl" for the English caption track. It converts that XML caption track into JSON, then searches it for keyword matches. You're right that this particular search for "toxic" should find several spoken word matches, but it doesn't. It seems like the tool isn't able to access the captions data for that video for some reason. I made a note of this bug, and I'll look into fixing it. Thanks for pointing it out, and for checking out VideoMentions Search!