Very interesting exercises – thank you for that! A small tip for all viewers as a supplement: In Cello-Technik by Gerhard Mantel, the topic of the 'crooked bow' is covered in detail. This refers to the technique where the bow placement – the position of the bow between the fingerboard and bridge – is deliberately changed. Mantel describes four forms of this angled bow: two starting from the frog and two from the tip – each with movement toward the fingerboard or toward the bridge. The bow deliberately follows an angle and thus follows the natural vibration of the string. On the other hand, if one tries to stay strictly parallel to the bridge (i.e., 'straight') when changing the bow placement, it hinders the sound development – the vibration can't spread freely. So the 'crooked bow' is not a mistake, but rather an important prerequisite for a rich and flexible bow technique. Even though your video primarily focuses on the topic of feeling and expression, the 'smile exercise' shown fits wonderfully under the term of the 'crooked' or 'wandering' bow – a technique that many teachers initially prohibit for beginners, because the straight bow stroke (90° to the string) is actually the greater challenge. Maybe this would be an interesting topic for one of your upcoming videos!