I noticed if I hit a shielded enemy with a boomerang (I modified the enemy so it can be damaged by a boomerang of a level greater than 1) while on a conveyor facing left (it might also happen on other conveyors but I only tested left) the enemy sometimes gets damaged by the boomerang even though I am hitting their shielded side. Sometimes it damages them and sometimes it doesn't but it always plays the "clank" sound that plays when you hit an enemy shield. Here's a short video I made showing it. Sorry about the lack of audio, but as I said it plays the "hitting shield" sound every time the boomerang hits the enemy, whether they take damage or not. You'll notice part way through that I hit the enemy a few times while not moving vertically, just letting the conveyor take me left, and the enemy sometimes takes damage and is stunned, and sometimes they block the boomerang.