عند حضور المشبه
When the subject of comparison becomes present to the mind.
An important feature of a familiar simile is that thinking of the subject readily evokes the comparison term. A luminous face, for instance, commonly evokes the moon in certain literary conventions. This is about the movement from subject to model, not merely knowing both words.
A comparison model may itself be well known without immediately seeming relevant to a particular subject. Familiarity with the model alone is insufficient; the resemblance in this context must also be apparent.