Pulling faces

[rebbonk]

Finding one of her students making faces at others on the playground, Ms. Smith stopped to gently reprove the child. Smiling sweetly, the Sunday School teacher said "Bobby, when I was a child, I was told that if I made ugly faces, it would freeze and I would stay like that".

Bobby looked up and replied "Well, Ms. Smith,

Spoiler:

you can't say you weren't warned".