Just a quick update: This morning my kitten went for a poo with both back legs inside the tray, but she's still standing up to go instead of squatting, so she made a bit of a mess of her bottom but her leg remained clean (her poo is not runny or loose in the slightest). Something kateyblue stated eariler got me thinking, though: "If not and she's having difficulty passing poo then maybe in that position she's more comfy." All this balancing stuff started within a few days after she'd been spayed (she was spayed 10 days ago). Could she be finding it difficult to strain since being spayed, or maybe her tummy is unomfortable at the scar, or something? Should I contact her vet?