A little bump in my dog's crotch

My mom told me the last day that my dog has something in his crotch, today i kinda touch him and is like a little ball, is not that big, i touch the other side of my dog to look for the same little ball and there is nothing there. Looks like the bump does not hurt him cuz when i touch it seems that he was ok with it. there is no anomaly in his skin in that area, the bump feels firm, like 1cm diameter. and i dont know if i am exaggerating but i kinda also notice that he walks funny... whit his "legs" kind of very open.

[Aleda M Cheng, D.V.M., C.V.A]

Any bump or mass should be examined and biopsied by a veterinarian.  Many dermal masses or bumps are benign lesions such as lipomas (fatty tumors) or sebaceous cysts but a biopsy must be performed for a definitive diagnosis, since malignant tumors can mimic benign tumors.  

There are other causes for lumps also, such as insect bites, traumatic injuries,  or even a foreign body under the skin such as a splinter.  These too should be investigated by a vet if they don't resolve quickly.