As with any injury, there are so many variables involved, like age, weight, species/breed of animal, and the type of impact or injury that caused the lameness.
The goal of this article is not to provide a self-diagnosis of what is wrong if your pet is lame. Rather, this can help pet owners identify when an injury is an emergency or if it can wait a bit for observation at home.
Answer: Soft tissue swelling could mean a few things: insect bite or sting, infection and abscess, or blunt tissue damage.
Bee stings can produce a huge swelling very quickly but aren't usually too painful. (Cats are generally more prone to getting insect bites/stings on their paws from batting at bugs, whereas dogs typically get swollen lips from trying to snap at the bugs.) This is an allergic type of reaction, and if it doesn't get infected, will go down in 24 hours or less. Your veterinarian can administer or recommend medications to help reduce swelling and stop the allergic reaction.
Other bites/stings, such as those from spiders, scorpions or other insects can produce painful, nasty swellings with tissue necrosis (death). It is wise to call your veterinarian as soon as you notice any swelling on the paws or elsewhere.
Punctures, bites, and other tissue trauma can also produce large swellings that are infected (pus-filled). These swellings are often are painful, depending on what stage of infection. Call your veterinarian as soon as possible, medications to treat each condition are different, and if untreated, can get considerably worse in a short time.