ухмыльнуться bedeutet auf Englisch

grin [grinned, grinning, grins]▼(To smile showing the teeth)
verb
[UK: ɡrɪn] [US: ˈɡrɪn]

smirk [smirked, smirking, smirks]▼(to smile in a way that is affected, smug, insolent or contemptuous)
verb
[UK: smɜːk] [US: ˈsmɝːk]