When they are searching for Reggie, Maggie has to sniff the bandanna he left behind so she could get his scent. But she had been with him the previous 48 hours, and it had only been less than an hour since Reggie had left.
When Reggie is about to bite Doug's penis off as he is laying on the ground, Maggie and Bug grabs his legs and open them up for Reggie so he can bite it off easier. However, in the shots where he actually starts to bite it off, you can clearly see that his legs are no longer held by Bug and Maggie in the background and are actually free, even though there are shots after this that shows them still holding them.
Maggie is a female dog, but she always pees forward instead of backwards.
It is lovely that Maggie, an Australian shepherd, is voiced with an Australian accent. However, the breed was developed in the USA and is wholly an American breed.
The "narrator" dog, voiced by a male actor, is clearly played by a female dog.
Despite being strays, all of Reggie's friends look clean and frequently groomed.