There's a startle of surprise that Astarion can talk to him like that; Arthur can't. He has to speak out loud to him, and that's been inconvenient more than not. But with the wonders of the tadpole have a fun unexpected result.

Astarion will feel that delight before he answers.

[Yesss.]

That is a deeply satisfied eldritch horror. Comfort filters out from him; he wouldn't keep that from Astarion.

[Don't worry; I can follow your stride after a few steps. I'll move your arm in time.]