[levocardia]

Real answer: how many animals can you think of with three legs?

[pphysch]

There are millions or billions of quadrupeds surviving on 3 legs every day. 4 legs is evolutionarily superior to 3 but 3 gets the job done, especially if you don't have to worry about agility or repair.

[wat10000]

How many animals have wheels? And yet wheels are a pretty practical choice for a lot of things.

[bensyverson]

Ah, so it’s impossible to make a robot unless it looks like an animal

[Y_Y]

This one right here

[scotty79]

Kangooroos?