Four Types of Learners

From the Mishnah:

There are four traits among those who sit before the sages:
a sponge, a funnel, a strainer, and a sifter.
A sponge—because he sponges everything up;
a funnel—because he takes in on one side and lets out on the other;
a strainer—for he lets out the wine and keeps in the lees;
and a sifter—for he lets out the flour and keeps in the finest flour.

(Avot 5:15)