A guy in glasses is biting into a pink marshmallow chick while somebody else is puckering their lips out wanting a bite.
A guy bites into a marshmallow while someone else desires a bite
If a guy bites into a marshmallow while someone else is puckering their lips, they desires a bite.
Someone is a synonym of somebody, and desires means a person is wanting something.
someone puckering their lips out wanting a bite can be rephrased as someone desires a bite