There's a first for every question. The Q and my A:

I have a question though about a combat action that does not seem to be included in the rules. I have seen official GURPS rules that cover this technique in only one book, GURPS Bunnies & Burrows, in which the maneuver is called "Ripping".

The basic idea is that a bunny (and presumably other similarly built animals) can grapple a foe with its front paws and/or teeth, and then use its hind legs to rip into a foe's torso. In B&B's game terms, once a foe is grappled, the rip is done at skill-2, the defender is at 1/2 dodge, and the rip does thrust+1 cutting.

Are there rules which would cover this sort of situation embedded deep within the GULLIVER rules?

Not really, but is something additional needed?

The only addition that I can think of, if you wanted lots of detail, is modifying damage for weight: a heavy foe on top of you, ripping, can really "dig in". Book 5, under weight and damage, has rules for a weight-based bonus for stomps; seems that could apply here.

(If the ripper were on his back, and the target *on top*, then the target's weight would determine the extra damage...)

If so, can you point me in the right direction? If not, do you have any general ideas about how to handle a move like this, particularly when it comes to attempting to rip a target of different size?

I guess the key is whether shape and size allow the move to work at all. Cats and rabbits seem to have no trouble getting their back feet way up towards their own stomachs or chests, and so I assume they can reach those spots just fine on the victim too, when in the rip "embrace".

But if the target were a Size level smaller, its stomach and chest are going to be moved up higher; maybe the attacker could only rip at its legs?

And if the target were two or more Size levels smaller, maybe the attacker's feet wouldn't reach it at all. Unless he pushed the target down to where the feet are, but then he wouldn't be holding the target any more, so it might get kicked away after the first rip.

Going the other way, I don't see any problems with ripping at a creature bigger than yourself.

Finally, creatures with other shapes may not be able to rip effectively; a human with clawed feet would have to be pretty flexible to rip even a same-sized or larger target. Sounds like a big penalty to me.