If you weren't charged extra for the special topping then you should consider it a freebie, I wouldn't say anything about it to management or someone could get into trouble for accidentally including it on your order. If it were me I'd just go ahead and enjoy the tasty free topping and never mention it again.
Be careful they will threaten to have you arrested if you bring their scrappy food back!!
The manager ! Where you got your pizza.
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