A bride who can't make herself walk down the aisle at her wedding; a person who has paid a lot of money for a skydiving trip who then won't jump out of the plane; a person who requests a karaoke song, but then doesn't want to get up to sing: What do they have in common? Cold feet.

In English, we say someone "has cold feet" when they suddenly get nervous about doing something they have planned. The phrase describes a situation where someone is afraid to do something he or she was previously excited about. Usually, it means the fear is unjustified, people usually get over their cold feet because their desire is stronger than their fear.

The term "cold feet" is an idiom, but is it based in reality? Research says yes. The American TV show MythBusters put three people in situations that scared them and measured the temperature of their feet. One took a scary stunt plane ride, one was covered in spiders, and one ate some insects. For two out of the three, the temperature of their feet dropped sharply when they became afraid.

The researchers think this has to do with something called the "fight or flight" response. When we're scared, our body prepares to fight or run away. More blood goes to our muscles, preparing for action. In our skin and other organs, blood vessels constrict, so we'll bleed less if we get injured. When the fight or flight instinct kicks in, the small muscles in our feet get less blood. This means our feet often really do cool off when we're afraid.

Should we wear thick socks when we think we'll be nervous? Probably not. Push through your fear and your chilly feet will be just fine.

走上紅毯前那一刻想落跑的新娘、斥資參加跳傘之旅卻腳軟無法跳出機門的人、到卡拉OK 點歌又不敢上台獻唱的人，這些人的共同點就是所謂的「臨陣脫逃」（cold feet）。

英文裡說的「cold feet」，是指一個人原本計劃好要做某件事，卻突然緊張而想臨陣脫逃的情況。這個片語描述一個人不敢做他原本期待的事。這種恐懼通常是莫名的，往往內心的渴望必須大於恐懼感才能克服這種cold feet。

「cold feet」一詞是個俚語，不過是否有事實根據呢？研究顯示真有其事。美國電視節目《流言終結者》讓三個人處於自己所懼怕的環境裡，並且測量他們足部的溫度。一位搭乘驚險刺激的特技飛機，一位讓蜘蛛爬滿全身，另一位則吃昆蟲。其中兩人開始害怕的時候，足部的溫度也驟降。

研究人員認為，這跟所謂的「對抗或逃避」反應有關。我們害怕的時候，身體會做好要對抗還是逃跑的準備。這時更多血液進入肌肉，以應萬變。而皮膚與其他器官裡的血管則會收縮，以減少萬一受傷的出血量。當對抗或逃避反應啟動，腳部的小肌肉所獲供血量減少。表示說，我們害怕的時候，足部真的會降溫！

那麼當我們覺得會緊張的時候，是不是應該穿上厚襪子呢？大可不必。咬牙克服自己的恐懼，冰腳丫也就沒事了。