Thanks for playing! I think I'll definitely revise some of the controls in a future update. An aiming arrow sounds like a really good addition, maybe show it on mouse press and hide it again on release?
I'm pretty surprised to hear that rats can collect power-ups, but I just had a look at the code and yep, it's totally allowed. That's a really funny bug. Might be fun to keep a version of it as an event where a rat steals a power-up from you and you have to chase after it to get it back.