On a stormy day, taxi cabs are as scarce as hen's teeth.

在暴风雨的日子里，计程车几乎看不见。

Not only were qualified interpreters as scarce as hen's teeth, but the gap in mentality was a million miles wide.

这不仅是因为那时合格的译员凤毛麟角，而且还因为双方的思维方式也相差十万八千里。