I worked for many eateries over several years and could probably write a book of disgusting stories. I'll spare you the worst but I'll tell you about the time I was working in a fried chicken restaurant and, along with the batch of chicken I'd just prepared, I'd unknowingly batter dipped and deep fried a frozen mouse.
The lady working the drive-thru was filling an order, noticed it and told me about it. At first, I didn't believe her but I looked in the warmer, pulled out the tray and, sure enough, there it was. That batch was thrown out along with the flour mix and water. I'm just glad she caught it in time. I was triple-checking every bag for months after that.
Mild compared to a now-defunct cafeteria where I was the porter. The things I saw there defy belief. Really don't want to go there though.