This episode is all about trills. Trills can be a great way to train the hand and build up stamina. In the Beethoven concerto, some trills go on for a very long time, and have to sound continuous and almost timeless this really tests our endurance, and it's important to find a way to trill that isn't too tense.
But trills can have other shapes too. Rather than thinking of trills as having an "on" and "off" switch and always starting fast, they can start slowly and speed up, or start after the note (or not go until the end of the note) depending on what is musically appropriate. I give an example of a trill in a lyrical passage, and how to shape it so it can be expressive.
In another example, from the Brahms concerto, the trills are fast and gruff, and used to emphasize and accent the notes.
Every trill is different!