Yeah, we had a really tough time figuring out how to communicate that to the player. We animated circles shooting out between the gun and the target and added expository text a couple times mentioning "exchange", but what we really needed was a way for the player to see when an object actually had a size multiplier or a speed multiplier on it! Then you would know that "oh, if I shoot that I can exchange my current size multiplier for that one". As is, it's not clear to the player why some objects don't interact with the phaser.
Thanks for playing!