[Shaun]

Why, when crying, does one's lip/jaw start to tremble?

-just watched the scene from Up where Ellie finds out she can't have children and they get old and yeah-

[Smithy]

do it yourself you lazy sod

But that film

[Shaun]

I thought I'd get a topic out of it

[Ninastar]

maybe cause you're trying not to frown?

idc, it's a good question

[Brother Leon]

Your lips are trying to dance away the tears.

[Glenn.]

Your bottom lip is controlled by the parasympathetic nervous system which also controls the tear ducts and throat.

I googled it