tun-a-fish, get it?

The on-line manual pages of the original tunefs, like all Berkeley commands, ended with a "Bugs" section. In this case, it read:

Bugs:
This program should work on active and mounted file systems, but it doesn't. Because the superblock is not kept in the buffer cache, the program will only take effect if it is run on dismounted file systems; if run on the root file system, the system must be rebooted.
You can tune a file system, but you can't tune a fish.

NAME
    yesterday – print file names from the dump

SYNOPSIS
    yesterday [ –abcCdDs ] [ –n daysago ] [ –date ] files ...

BUGS
    It's hard to use this command without singing.

http://plan9.bell-labs.com/magic/man2html?man=yesterday&sect=1