As an aside, my wife and i were having trouble conceiving, so i bought a cheap microscope just to sanity check that my sperm were alive and kicking.

Of all the things my kids and i have looked at under the microscope, sperm is some of the most entertaining to watch.

While it's obviously not a definitive measure of fertility, you can tell a lot by just observing them, and seeing at seemingly millions of sperm going crazy took the stress out of trying and we became pregnant soon after.