Stroking a pet cat is missing its animation.
What I did: I used the 'Stroke' interaction option with a pet cat.
What I expected to happen: I expected my character to pet the cat and to have the cat reciprocate.
What actually happened: The cat stood there as my character used the animation for setting the cat down.
IDs of related NPCs/items: NPC ID: 770 and likely all other cats. Unfortunately, I do not know where to find these NPC IDs without raising every kitten, but their item IDs are as follows: 1561, 1562, 1563, 1564, 1565, 1566.
2009-era source (if relevant): https://web.archive.org/web/20090226184502/http://runescape.wikia.com/wiki/Cat (includes a .gif of the animation in question)