[kps]

Late versions of Eudora added something they called ‘mood watch’, which could highlight potentially inflammatory words or phrases (including profanity) in email and warn you before sending. The developers added a hidden setting which would, when you opened a message, speak aloud precisely those words.

[alexpotato]

And of course there is a relevant XCKD for this: https://xkcd.com/481/

[kps]

In response, YouTube actually implemented this (though only as an option, and it's since been removed): https://blog.xkcd.com/2008/10/08/youtube-audio-preview/