Experts say they have proved for the first time that dogs know how humans think.
Researchers from the University of Portsmouth got 86 dogs and their owners to take part in an experiment.
The owners and their dogs took it in turns to go into a special room.
Inside it there was a bowl of dog food, but the owners had to tell their pets not to eat it.
In most cases the dogs were good...
But the trick was to see if they would still do as they were told if the lights were turned out.
The study showed the cheeky animals were four times more likely to be naughty - and steal the food - when the room was dark.
The researchers said this meant the dogs knew that their owners couldn't see them eating the food in the dark.
"Whenever my brother and I are upset my dog comes up to us and licks our face to make us feel better so I think dogs do know how we are feeling."
Hattie, Leeds, England
"My dog listens to me as when I pat the sofa she knows she can sit next to me but she licks my feet which tickles a lot! So I think they do understand us."
Poppy, Essex England
"I think my Yorkshire terrier does know how I think because when I say dinner she pesters me until I give her hers!"
Sarah, Aberdeenshire, Scotland
"I think pets do know what we are thinking because when I get ready to go out my dog runs to the door just before I'm about to leave."
Shannon, Glasgow, Scotland
"I think dogs are very smart and would know what we think and do because they live with people all their life. My dog does many things such as picking letters up from the door and giving them to my mum."
Keira, Cardiff, Wales
"I think dogs understand what humans think and feel because if I'm upset my dog will comfort me. When I talk about going for a walk she knows that she can come."
Lauren, Durham, England
"I think they do because my dog knows when I am sad and she comes and sits by me to try and cheer me up by bringing me her toys and licking my feet to get me to giggle! She seems happy when it works and I smile at her."
"I think dogs understand what we say because when I say bath time he always runs upstairs and gets in the bath."
Becky, Surrey, England
"My dog runs to the door when we say cat and we've tried to stop him getting excited when we say walk so we spell it out, but now he under stands that!"
Josephine, Sheffield, England
"I think that dogs become familiar with commands and actions towards them that people do or say. They notice that they only get in trouble for sitting on the sofa if we are around or not looking. "
Orla, Houston, USA
"I think dogs know how humans think because when we talk to them they understand us."
"Nobody knows what other people think and dogs are a different species."
Sara , Dubai
"I think they do understand us because most of them have lived with humans most of their lives so they get to know how humans think."
Kara, Gloucestershire, England
"Humans know their pet's personality and how they think, so I think it's possible for pets to do the same."
Natasha, Denbighshire, Wales
"I think they do know. I have a dog and he always steals my mum's toy elephant when she's not looking!"
Charlotte, Reading, England
"I think animals do know how we think and they know if there doing something good or bad! For example, if they are doing something bad they stop what they're doing when they notice you."
Briana , Norfolk, England