In a kind of “sting operation” on the social media site TikTok, The Wall Street Journal created dozens of automated accounts, also called bots. They set up these bots to understand what TikTok shows young users. These bots, registered as users aged 13 to 15, were turned loose to browse TikTok’s videos. The videos revealed that TikTok can quickly drive minors (and of course adults, too) into “rabbit holes” of content focused on drugs, violence, or sex.

For example, one bot was programmed to dwell on videos with hashtags related to drugs. On its first day on the platform, the account lingered on a video of a young woman walking through the woods, with a caption suggesting she was in search of marijuana.

The next day, the account also watched a video of a marijuana-themed cake. Soon after, the teenager’s feed took an abrupt turn … with the majority of the next thousand videos touting drugs and drug use, including marijuana, psychedelics, and prescription medication. One showed an image of a person exhaling smoke and linked to a website that was “420 friendly” (code for marijuana use) and offered “yummy goodies for all.”

The article concluded that TikTok only needs one important piece of information to figure out what a user wants: The amount of time you linger over a piece of content. Every second you hesitate or re-watch, the app tracks you. Through that one powerful signal, TikTok can learn your most hidden interests and emotions, and drive users of any age deep into rabbit holes of content—in which feeds are heavily dominated by videos about a specific topic or theme. It’s an experience that other social-media companies like YouTube have struggled to stop.