wrinkle your forehead
The phrase 'die Stirn runzeln' is a German idiom that literally translates to 'wrinkle your forehead'. It is used to express confusion, doubt, or disapproval. It is often used in situations where someone is trying to understand something or is not sure about a particular situation.
He will frown when he sees this.
This sentence is in the simple future tense, expressing an action that will happen in the future. Here, the verb 'runzeln' (to frown) is combined with 'die Stirn' (the forehead) to describe the action of frowning.
She frowned when she heard the bad news.
This sentence is in the simple past tense. It shows a moment when the action of frowning (represented by the verb 'runzeln' combined with 'die Stirn') occurs at the same time as another action (hearing the bad news).
I often frown when I solve a puzzle.
This sentence is in the present tense, expressing a habit or something that regularly happens. The phrase 'die Stirn runzeln' (to frown) is used here to express the speaker's reaction when doing a particular task (solving a puzzle).