•she smiled
•he smirked
•he simpered
•she beamed
•her mouth curved into a smile
•the corner of his mouth turned up
•the corner of her mouth quirked up
•a corner of his mouth lifted
•his mouth twitched
•he gave a half-smile
•she gave a lopsided grin
•his mouth twisted
•he plastered a smile on his face
•she forced a smile
•he faked a smile
•her smile faded
•his smile slipped

•he pursed his lips
•she pouted
•his mouth snapped shut
•her mouth set in a hard line
•he pressed his lips together
•she bit her lip
•he drew his lower lip between his teeth
•she nibbled on her bottom lip
•he chewed on his bottom lip

•his jaw set
•her jaw clenched
•his jaw tightened
•a muscle in her jaw twitched
•he ground his jaw

•he snarled/his lips drew back in a snarl
•her mouth fell open
•his jaw dropped
•her jaw went slack
•he gritted his teeth
•she gnashed her teeth

•her lower lip trembled
•his lower lip quivered