You might try a bit of ignoring of the behavior. Two-year-olds can be interesting that way. My son developed a "limp" about that age that was highly convincing, although not constant and he didn't really complain of pain. After doctors visits, x-rays, bone-scans, etc. and finding absolutely nothing wrong, we took the stance of simply ignoring it and it went away without the attention he was getting. We think it was something he picked up simply from watching his father walk (his dad has a physical condition that creates a limp).