Sentence:  If life seems jolly rotten / There's something you've forgotten / And that's to <WSD>laugh</WSD> and smile and dance and sing. 
Meaning of the word marked with <WSD> tags:  To show mirth, satisfaction, or derision, by peculiar movement of the muscles of the face, particularly of the mouth, causing a lighting up of the face and eyes, and usually accompanied by the emission of explosive or chuckling sounds from the chest and throat; to indulge in laughter.