We'd like to think we walk through our lives completely conscious（意识到的）, free to choose whatever we like, totally completely in control. Not even close. Our bodies leave a lot to autopilot, which is a good thing because imagine having to regulate（管制） your heartbeat（心跳） and your breathing and your digestive（消化的） system and your body temperature, all while not peeing your pants and falling down. That would be hard. Many of those involuntary actions are mysterious（神秘的）, annoying, and just plain weird（怪异的）. Here are five of the human body's strangest out-of-control behaviors.

  Start typing "why does my" into Google and the top result is an eye opener. Involuntary twitching of the muscles around the eye has a number of causes, including dry eyes, caffeine, bright lights, and just like during a tough（坚韧的） workout（锻炼）, from simple fatigue（疲乏）. It's usually totally harmless and eventually goes away on its own, and it's a good hint（暗示） that you've probably been looking at that screen enough for one day. Looking at bright light can cause more than an eye twitch（抽搐）. In Aristotle's book of problems, he asks, why is it that one sneezes more after one has looked at the sun? Proving that people have been asking a lot of the same questions for a long time, and no one told Aristotle that you're not supposed to stare（ 盯着看） at the sun, like ever.

  The so-called "photic sneeze reflex" aka the autosomal cholinergic helio-ophthalmic outburst, abbreviated（ 缩短） "achoo," yes, seriously, is experienced by about one in four people, leading scientists to believe that it is genetically heritable. While the exact cause hasn't been pinpointed（查明）, many scientists think that it's due to crosstalk between the optic nerve（神经） and the nerve（神经） that feeds the tickling sensation（感觉） in your nose. The visual（视觉的） cortex（(植物的)皮层） of sun-sneezing people is also prone（倾向于） to overstimulation, which might send the sneeze-sensing（感觉到） parts of their brain haywire. Have you ever been just about to go to sleep, walking through the gates to dreamland, only to have the floor pulled out from under you and suddenly you're falling and then you wake up? These frustrating（令人沮丧的） sleep starts have another cool medical name, hypnagogic myoclonus. When we drift（漂流） off, the areas of our brain that control motor（发动机） function are inactivated（使不活泼） in favor of those that control our sleep cycles, which is why you can dream about riding your bike without actually moving your feet.

  As the sleepy part of your brain fights with the awake and moving parts of your brain, that battle can spontaneously（自发地） tip back（在后） in favor of the motor（发动机） control side and then suddenly you're like, whoa, awake. Sleep starts aren't the only myocloni that we experience. Hiccups（打嗝） are an uncontrollable contraction（收缩） of the diaphragm muscle that we used to draw air into our lungs（肺）. About a quarter second after that muscle contracts（合同）, the vocal（歌唱的） cord（细绳） snaps（猛咬） shut, creating that characteristic（典型的）. Scientists still aren't sure what causes them, but possible explanations include hiccups being an evolutionary（进化的） remnant（残余） from a few hundred million years ago when our ancestors（祖宗） still had to pump water over their gills. Or since hiccups mainly happen in mammals（哺乳动物）, that they started as a way for nursing（护理） infants（婴儿） to clear air from their stomachs.

  If you want to get rid（使摆脱） of hiccups（打嗝）, it seems that increasing the amount of CO2 in your blood can do the job, which is why common remedies（治疗） include drinking water, holding our breath or breathing into a paper bag. Yawning, another long, slow, involuntary form of breathing, is common throughout the animal kingdom（王国）, and it even happens in the womb. We know it's associated（交往） with sleep and boredom, but that doesn't explain why it happens, and like most human behaviors, if you stop and think about yawning long enough, it starts to become a really weird thing to do. Hippocrates believe that yawns released noxious（有害的） fumes（(浓烈或难闻的)烟） that had built up in the body, but modern medicine has shown us that that usually happens on the other end of the body. We also know that about 50% of people who observe（遵守） a yawn will yawn in response, so it's thought to be a social cue（提示） to synchronize（同步） our biological（生物的） clocks. One theory says yawns might even cool the brain slightly to make us more alert（警惕的） as we get bored or sleepy.

  Even watching someone talk for extended periods of time can induce（劝诱） yawning. So next time you're getting bored in class, tell your teacher it's mother nature's fault（过错）. Finally, I'll leave you with one bonus（奖金） behavior, Post-Micturition Convulsion Syndrome（[临床] 综合症状）, or the P-Shivers. This is another behavior for which scientists haven't quite shaken out all the details, but some believe it's simply because we're exposing（使暴露） sensitive（敏感的） areas of our body to the cold while we expel（驱逐） some internal warmth. They might also arise（出现） from a bit of conflict（争论） between our autonomous nervous system that's usually quietly keeping all that pee inside and the part of our conscious（意识到的） mind that's in charge of the plumbing at that moment. These weird, wild, and often twitchy behaviors may define nice neat（整洁的） explanations, and yes, sometimes they are very annoying.

  But in the great movie that is life, they're a nice reminder（ 提醒物） of all the amazing things going on behind the scenes.