May be shown, not necessarily with a smile! (5)

I believe the answer is:

teeth

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'smile' is the definition.
The definition and answer can be both related to bodily activities as well as being verbs in their base form.
Maybe you can see a link between them that I don't see?

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for teeth that I've seen before include "Projections on a gear" , "Cog wheel projections" , "Power to enforce" , "Food may get stuck in them" , "Fangs" .)

I've seen this clue in the Evening Standard.

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