Sentence:  She's got a perfect <WSD>smile</WSD>.  He has a sinister <WSD>smile</WSD>.  She had a <WSD>smile</WSD> on her face.  He always puts a <WSD>smile</WSD> on my face. 
Meaning of the word marked with <WSD> tags:  A facial expression comprised by flexing the muscles of both ends of one's mouth, often showing the front teeth, without vocalisation, and in humans is a common involuntary or voluntary expression of happiness, pleasure, amusement or anxiety.