Thank you for playing and commenting.
I'm thinking of adding some sound for soul vacuuming, but I haven't come up with something concrete that convinces me and isn't too annoying for the player (especially when the screen is full of souls).
Yes, by holding down the button, you vacuum temporarily. The cloud aspiration upgrade allows you to extend the vacuuming time, and at its maximum level, it allows continuous vacuuming without a cooldown.
All upgrades have a maximum limit. I'll balance and improve this in future versions of the game