What's the meaning of "they went through the rodent equivalent of withdrawal"? You may love to soak up the sun—or the UV rays at the tanning salon. But are you actually addicted? A study finds that mice regularly exposed to UV produced the feel-good opioid β-endorphin, and behaved like addicts. What’s more, when they were given a drug that blocked the opioid effects, they went through the rodent equivalent of withdrawal: shaky paws and chattering teeth. The study is in the journal Cell. What's the meaning of "they went through the rodent equivalent of withdrawal"?