Your phone isn't secretly listening to you, but the truth is more disturbing

One time my wife and I had a random conversation, utterly random, about cat hamster wheels. Like, why doesn't that exist? I got an ad for it the next day (it exists).

I don't believe that my phone is not listening to me and I challenge you to choose a random word out of the dictionary and say it 100 times in front of your phone.

A few times per year I similarly have a conversation with my wife at night (lastly about a hair type) and the next morning a corresponding ad was presented at her at Facebook (shampoo). Only her Android phone was at the room (open, logged in Facebook in Chrome, no app). I definitely believe they hear us but they trigger the action with care and selectively, so as not to get caught (eg to low tech people, when the ad is very relevant to the need etc).

I am astonished that nobody had ever done a reverse engineering research yet.