We have an idiom in Urdu that could be translated as, "cat always dreams of meat". The meaning is something like, "one always sees what one desires".
Let me try to put it in a context. Suppose,
A group of friends was planning to visit one of their acquaintance to condole for her fathers death. Another of their friend approaching towards them, while catching part of the discussion, and exclaimed, "Hey, I'd love to join you guys, her mom makes fantastic croissants" — having no knowledge of her father's death.
Now here we can use this, "cat always dreams of meat".