Mice Versus Lawyers

At a convention of biological scientists one researcher remarks to another:
"Did you know that in our lab we have switched from mice to lawyers for our experiments?"

"Really?" the other replied, "Why did you switch?"
"Well, for four very good reasons. First we found that lawyers are far more plentiful, second, the lab assistants don't get so attached to them, third there are some things even a rat won't do, and fourth sometimes it very hard to extrapolate our test results to human beings."