type of litter – some cats prefer clumping to pellet or crystals, and others like my Trikki lion are okay with #1 in any type of litter but only clumping will do for #2. Some litter scents/perfumes can be off-putting as well.
Litter box – # of boxes, cleanliness, placement, covered vs uncovered.
Spraying and Marking
Stance - the cat will emit small amounts of urine, and typically have an erect tail with some level of quivering with his/her back up to a vertical surface e.g. a wall or edge of furniture.
Location - less likely to be in out of the way spots, more likely to be around/on the human whose attentions might be divided among other cats, and/or a rival cat/other animal.