17. A Night In Sickbay (ENT)
"The Kreetassans consider the Alvera trees cultural treasures. Apparently, Porthos urinated on one of them."
I'm not the first one to make this pun, but it's so easy, I'll do it. This one is just a dog. What's it about, you ask? After botching a diplomatic mission, Archer learns that his beloved beagle, Porthos, contracted a disease while on the planet (because Porthos comes along for important diplomatic missions, you see). Archer is furious, because the aliens of the week didn't warn him that Porthos could get sick.
The rest of the episode sees him spending a night in sickbay with his trusted dog while Phlox tries to find a cure before it is too late (spoilers: the dog makes it). Oh, and that diplomatic mission I mentioned? Archer blew it because he couldn't control his pet beagle, who peed all over one of the Kreetassans' sacred trees. Whoops. If only that could have been avoided somehow.