Small issue: the game sometimes slows down when you are able to level up but are still using hearts. I assume related to multiple animations, as it clears up as soon as you do level up.
Also can someone tell me what the occasional chirp when revealing an empty tile means? EDIT: I just made the connection on this one... obvious in hindsight that it's only empty tiles, but this seems more like flavor than some sort of indicator like I thought it was (unless perhaps, there is a meta-strategy possible).