As an RCA (Rural Carrier Associate) who just started working for USPS not long ago, I can tell you that there is a LOT thrown at you in the beginning, and until you learn your route and your case you WILL be slower than normal. It takes me 4-5 hours to leave the office because there is so much mail and sorting it takes so long when you don't have everything memorized. That being said, if I saw I had a live animal parcel, I would probably ask the supervisor to call the customer and explain the situation (giving them the option to come and pick it up rather than waiting for me to deliver it).

It's a stressful job though. Trying to get everything right, and get everything DONE, is next to impossible. I'm totally drained at the end of the day, just from the mental fatigue and from working a 12 hour day with only a 15 minute break to eat a sandwich (because I literally don't have time to take more breaks than that because the days are so long to begin with). There's no excuse for a lot of the things mentioned in this thread (like dropping something off at a random address because you don't know where it's supposed to go, nope, I would get fired for that, not okay), but I did want to mention that these jobs aren't easy and these postal/UPS/FedEx workers have a lot on their plate.