“Sheep” (oveja) you may well know. It is single and plural. For example, there is a sheep in the field, and there are 10 sheep in the other field (prado). Someone can also look “sheepish” meaning “avergonzado””. However, the interest in this article is the use of sheep in idioms (modismos).
Sometimes we have to “separate the sheep from the goats”, to separate some issues for clarity. Perhaps in Spanish you might say “separar el grano de la paja”.
A family member could be described as “the black sheep of the family” (ser la oveja negra de la familia), meaning that the person is very different from the family and is viewed negatively.
A boy could “make sheep´s eyes at a girl” (…con ojos de cordero…), meaning that he looks at her in an amorous and perhaps foolish way.