I haven't completely decided yet, but I'm thinking of having the next object emit a "scraping" sound as it moves/scales, that way the sound gives you a general idea of the vicinity of where you should be looking. It will take some experimentation to get the balance correct: too easy and the game isn't fun, too difficult and it's just frustrating and tedious.
Here is a tiny preview of the basic mechanics: https://youtu.be/cUU1HnT95RE