After rabies vaccination, the local arm swells up for the following reasons: 1. It is possible that the local injection of the vaccine into the muscle leads to a transient swelling of the local muscle, which usually subsides naturally after the drug is absorbed. 2. It is possible that the local puncture of the capillary is slightly larger during the injection, causing it to rupture and bleed, resulting in local swelling. 3. It is possible that the rabies vaccine drug has stimulated the local muscles or soft tissues, resulting in sterile inflammation of the local soft tissues, resulting in local edema and painful symptoms. In either case, the symptoms can be slowly relieved by resting or applying some heat locally.