Remember how Mom always told you not to get in cars with strangers? Ride-sharing services have turned that sage advice on its head.

It’s easy to see why. Using Uber or Lyft is far easier than trying to hail a cab on a crowded corner. Just whip out your phone, log in to the app, tap for a ride, and then pay for it with another tap when you’ve reached your destination. These new services are cheaper than traditional taxis, too.

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But there’s a dark side to ride-sharing services you may not be aware of, involving intoxicated passengers, bodily fluids, and worse. What do Uber and Lyft drivers know that you don’t? Plenty.

I talked to roughly a dozen drivers in different areas of the country and got the inside skinny. (All the names in this story have been altered to protect the identities of the drivers.)