Practical Joke

I used to work for a confectionery manufacturer and I have an admission. At social events it was often my practice to swap a real square chocolate with a mint filling (as illustrated) for a plastic one. Nestling in its little envelope it would await the unwary. Once chosen it would be carried to the mouth, bit into and ......... it would resist! There were inevitably laughs as I admitted that I was responsible. Well, as long as no one broke a tooth!