PENNY:Right. Okay,look,this is between you and me.
SHELDON: You're asking me to keep a secret?
SHELDON: Well,I'm sorry,but you would have had to express that desire before revealing the secret, so that I could choose whether or not I wanted to accept the covenant of secret keeping. You can't impose a secret on an ex post facto basis.
SHELDON: Secret keeping is a complicated endeavor. One has to be concerned not only about what one says, but about facial expressions,autonomic reflexes. When I try to deceive,I myself have more nervous tics than a Lyme disease research facility.It's a joke. It relies on the homonymic relationship between "tick," the bloodsucking arachnid,and "tic," the involuntary muscular contraction. I made it up myself.
PENNY: Okay,look,if Leonard finds out that I lied,I will absolutely die of embarrassment.
SHELDON: Physiologically impossible.
PENNY: Oh,Sheldon,please. Look,I am asking you as a friend.
SHELDON: So you're saying that friendship contains within it an inherent obligation to maintain confidences?
SHELDON: Interesting. One more question,and perhaps I should have led with this. When did we become friends?
LEONARD: You could be Batman?
SHELDON: Sure. I'm Batman. See?
1. impose on强加于利用；欺骗；
In a society with more and more obese people, this seems a costly burden to impose onthe airlines.现今肥胖人士越来越多，对航空公司来说是一笔昂贵的负担。
2. ex post facto事后的
No one can alter the fact, ex post facto .没有人能在事后改变事实本身。
3. nervous tic神经性痉挛,抽搐
4. make up捏造,编
I couldn't remember the fairy story I wanted to tell her, so I made one upas I went along. 我想不起我要给她讲的那个神话故事，于是我边讲边编了个故事。
5. lead with(报纸)把…作为重要报导(或头条新闻)
Today's China Daily led with President Bush's visit to China. 今天的《中国日报》以布什总统访华作为头条新闻。
6. start-up capital倒入资本,企业初期资本
With banks reluctant to lend, many entrepreneur have looked to family and friends for help providing start-up capital.因为银行并不愿意贷款，所以很多创业者纷纷转向了家庭和好友寻求帮助，以获得启动资金。