If it doesn't make sense, or your "Latin" is rusty, try reading it out loud.
O sibili si ergo, fortibuses in ero.And this other gem:
O nobili demis trux: sewatis enim? Cowsendux.
M R ducks.For that last one, you could replace ducks with rats or whatever, and get the same joke. Sure, they're groaners, but that's why we like them.
M R not ducks.
O S A R. C M wangs? C M E D B D I's?
L I B, M R ducks.
Speaking of Latin, my favorite doggerel as a student:
Latin is a dead languageAnd the esoteric: Conjugate the verb to spit
As dead as it can be;
First it killed the Romans,
And now it's killing me.
spitto, spittere, ach tui, splattus!