well if your talking Infectious Diseases then probably none but without regular excercise arthreitis can set in making it difficult for many animals to go about there regular routine.
yes they do , its in their front legs . LOL!
Echidnas have a tiny mouth and a toothless jaw.
No. Sea urchins are animals, which eat algae. They use there spines to make sure no fish eat them, and their mouths are on the bottom of them. They move around on almost invisible legs.
Lots of animals do have legs.
I believe they are called spurs -- at least in the case of cocks.
No. All Animals do not have 4 Legs
There are no known animals that have 12 legs. An insect does not have 12 legs, instead it has half, it has six legs.
because we humans walk on our legs and the animals don't have the sort of balance we have
all you have to do is exercise
Go EXERCISE
to work your legs
No, they don't usually enjoy them. Exercise balls can be dangerous, they are usually bad for their backs, so i wouldn't recommend using them. Instead I have a puppy pen that I put down in my living room on top of a blanket for exercise time! They have plenty of room to run around but can't get out and into trouble.