If there is anything that can prove particularly challenging to us cats, it is communicating to our humans what we need them to accomplish. While frustrating, it is not a hopeless cause, provided the humans in question are smart enough to understand simple, location-based hints.
Recently, I was able to indicate to the bearded one that it was time to clean my hygienic depository box by sliding my paws under the door of the closet where he keeps the plastic grocery bags used to throw out the scooped deposits, and by meowing as I looked at said door. The connection was by no means obvious, as said bags have other uses of less importance, and I love exploring the forbidden closet, darting inside at the first opportunity.
Therefore, as we can see, humans are capable of semi-complex logical processes, particularly if they involve a specific part of our abode or a particular item. Therefore, it is up to us to come up with new, creative ways to express our needs to our mostly-harmless staff.