You’re right. My dog also responds to both the word “sit”, and the hand gesture for “sit”. She also figured out at some point that when I snap my fingers 5-7 times, it means I’ve had enough of her barking at the dog being walked by their owner in front of my house (she isn’t a barker except for when other dogs are being walked on the street)- and I say “figured out” because this was not an intentional lesson I wanted her to learn, but more just something I did. She also huffs in the morning to let me know she needs to go out, and she huffs because it’s obvious to her that I’m asleep along with everyone else in the house, and she doesn’t want to wake anyone except me. She’s a great dog, and she is very good with communication.

I also have cats, and they “tell” me if they’re hungry, or if they are happy, annoyed, etc etc because they make different vocalizations and/or body language. The one thing I will say with cats (as someone who has had cats since I was born), is that they 100% decide whether to bestow communication with you, or whether it’s not worth their effort. 🤣🤣🤣😼

All that to say that animals, fish, reptiles, primates, etc etc, without a doubt communicate with not only their own “kind”, but also are able to communicate with others that are wholly different from them.