The adverb 动不动 “easily”
The adverb 动不动 
indicates that some undesirable action happens on every occasion and very quickly.
We should state the adverb 就 after 动不动.
indicates that some undesirable action happens on every occasion and very quickly.
We should state the adverb 就 after 动不动.Examples
他总是动不动就哭
He cries all the time
tā zǒngshì dòng bu dòng jiù kū
他要是睡眠不足动不动就发脾气
If he doesn't get enough sleep, he gets angry easily
tā yàoshi shuìmián bù zú dòng bu dòng jiù fā píqì
这个抽屉动不动就卡住
This drawer is stuck all the time
zhè ge chōutì dòngbùdòng jiù kǎzhù