Potassium cyanide. We used a very dilute form of it as a laboratory reagent (a safer alternative to its cousin hydrogen cyanide, in case that’s what you’re thinking of). It just smells clean - sort of like a candle that’s labeled as “fresh laundry” or “spring breeze”.
I bought some fancy biscuits for my dogs from a local company. Ingredients are basically oats, cheddar, bacon, rosemary. I could 100% kill this whole bag if my dogs didn’t look so devastated when I ate their special treats.