It could be anything. a zit, your spine or shoulder, or moles. there are probably others, but that's all i know of
It actually can be from the rear axle being too low to the ground. The back of the car hits the speed bump. That was the case with my bro's car anyway
It might be Syphilis.
i think if you have a bump on the back of your skull, you are getting a tumor.
When you hit the bump, the mouse wakes up.
check shocks
the bump after you get stung or bitten is caused by your body's immune system isolating the poison so it won't get into your blood stream
most likely your spine
no
A Pea sized bump on the back of an infant is called a hospital visit. Good luck.
My Bugdie had a big red bump on its back. We had to put it down.
check your shock absorber