First of all the "Humans as energy source" thing was a change that came from producers. Humans were originally being used as organic processors to augment the Machines' computing power, but execs thought that movie goers would be too dumb to understand that.

Second, by Smith's time animals didn't exist, due to the war with the humans, so it's doubtful he really knows much about them. It depends on how many human records were preserved by the Machines, but it's possible that accurate information on non-virtual animal behavior was lost.

Third, this is all just a speech he's using to break Morpheus. It's before Smith starts to get desperate, (and sends the other two agents out of the room) so it could be assumed that this is a practiced tactic that's work on other human rebels.

Finally, it's also somewhat ironic foreshadowing for what Smith becomes in the next 2 movies.