They are smart. I would say they are smarter than a cat.
Here are things they can do.
They can turn on water taps.
They can open doors.
They can identify buttons and push them.
Take lids off.
They learn words and vocabulary.
(They can learn their name, and words such as "no", "come" "get down" "give it back". But just because they understand the meaning of the word doesn't mean they will obey it.). If one starts to climb a peach tree to pick my fruit I will say "Hey! get down" as soon as they hear the words "get down" they huff then shake their head and try to get high enough that I can't pull them down by their tail.
When they are climbing a tree they have to hang on so gently pulling their tail downward makes so they can't turn and nip you and gently pulling on their tail will make them start climbing down backward.
If I say "Handsies'". they lift their hands... and I toss them a morsel...but only if they are in the mood. Most of the time they ignore it.
They seem to find pleasure and entertainment in doing something that they know will give them a reaction from you. Like grab your shoe and run off. Then they will get far enough away and turn to see if you are following.
