My guinea pig jerk quite often. It occurs when I'm looking at him. Any idea why?

Ivy Chiu Asked: My guinea pig jerk quite often. It occurs when I'm looking at him. Any idea why?I just got a guinea pig two days ago, and its about 5 months old. It started jerking suddenly when I'm looking at him. Initially, I thought that the hay might be tickling him thats why he jerk, but it doesnt seems like it. Sometimes, he also "clean" himself by using his leg scratch (just like how a dog/cat normally do). I'm afraid that he's gotten fur mites. Can anybody help

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