Spasms More Condition_symptoms Why Is My Rat Having Involuntary Spasms In His Tail?

Why is my rat having involuntary spasms in his tail? - spasms more condition_symptoms

My 1 1 / 2 years young rats began to have involuntary spasms in the queue. Little by little, was always more frequent. It will be good for a moment and then the tail is very fast and then press more. The rest is rarely moves. I checked everything and it looks good. He eats and is operating normally. His attitude has not changed. Besides being annoying, it does not seem to affect you. Why is this happening?