猫腻儿的英文：
illegal deal
underhanded activity
something fishy
dirty trick

illegal是什么意思：
adj. 违法的
n. 非法移民

They are illegal immigrants.
他们是非法移民。

Illegal immigrants or workers are sometimes referred to as illegals.
非法移居的移民或工人有时也被称为非法移民。

It is illegal to drink underage in America.
在美国，未到年龄喝酒是违法的。

deal是什么意思：
v. 处理；对付；交易；有关联；发牌；给予；分配
n. 交易；待遇；数量

Democrats usually do. They deal with labor, they deal with people.
民主党人通常都是这样的。民主党人和劳工打交道，和人民打交道。

To administer or deal out.
管理；分配

repeat an order, a deal
再次供应同样一批货、 一笔交易.

underhanded是什么意思：
a. 秘密的,卑劣的,人手不足的

It is a sneaky and underhand way of doing business.
这种做生意的方式偷偷摸摸，遮遮掩掩。

To attack,damage,or destroy by underhand means;subvert.
颠覆，暗中破坏通过隐蔽的手断进攻、损害或推毁;颠覆

Yes, I admit I've done some underhand things, but only on a very small scale, never anything serious
我用过一点手段，只不过一点，并未‘到处’用手段。