@JeremyECrawford Not sure if you've been asked this before;Can you perform somatic components of spells with a hand holding an arcane focus?
— Joshua Klein (@JoshuaKlein17) January 2, 2016
A hand with a material component, including a spellcasting focus, can perform somatic components (PH, 203). #DnD https://t.co/Rvbb93xFD7
— Jeremy Crawford (@JeremyECrawford) January 5, 2016
But if the somantic requires finger movements with the hand holding an object, I would say that is a no go!
The distinction is that the gestures/motions required for a spell that includes a material component are not as involved as with non-material-but-still-somatic spells. (That is, if you need to hold a ball of bat guano and there’s a somatic component then that latter aspect can be understood to be swirling it in a circle, making a symbol in the air, what-have-you, vs the more involved gestures that a straight-somatic spell might include.)