When the children were young we used to visit the children's wards as a family on Christmas day. One year the nurses gave my son a cracker that contained a grotesque looking pair of red plastic lips (red nose day had not yet been thought of). He entered into the spirit of the occasion, toddling around and displaying his lips for all to see. He knew how to use them, bestowing kisses on all and sundry.
The next day he developed mumps.