Is Your Bunny in Pain?
Your rabbit exhibits symptoms of pain by hunching up in the back of his/her living quarters or in a corner, grinding his/her teeth, not being as active as usual, not grooming him/her self or other companion rabbits, not being inquisitive, not responding to a favorite treat, and/or not eating or producing fecal pellets (not pooping).
⇒ "Pain in Rabbits: Assessment and Relief" by Maria Parga, MRCVS.
Rabbits in pain can become aggressive with other companion rabbits or their humans, especially when being picked up. Hunching and tooth grinding is particularly associated with abdominal pain. Pain associated with urinary problems causes a rabbit to strain and appear uncomfortable.
Giving aspirin for pain remains controversial. Most agree that a small amount of baby aspirin (dosage: 5 lb baby = 5 lb rabbit) is okay in a situation where you can't get your rabbit to a vet for several hours and you need to provide relief for your rabbit until you can get other medication.