«هِيَّ تِحْلِبِ الَّا لَمَّا يْكُونْ لَهَا بَو؟»

The image comes from dairy herding. A cow often withholds her milk unless reminded of her calf, so herders kept a calf's hide stuffed with straw nearby, not a living calf, to coax the flow. The rhetorical question expects the answer no: she would not yield milk without that prop.

Applied to people, it describes someone whose generosity or effort has to be set off by an outside trigger. Such a person waits for a reason, a reward, or a stirring of feeling before they give or act. The remark can sound wry, resigned, or mildly scornful.

Said of someone who will not give, help, or work unless a motive is placed in front of them, such as a reward, a pressing need, or an emotional pull. It can be dry or reproachful, and applied to a person it may sound like criticism of their character.