Sylvie cannot wait to get home from school to play with the puppy she was given for her birthday. The moment she opens the door it will come rushing down the hall and jump up at her. What a happy animal!

Or is it? After all, it could be that the puppy is wild with frustration after being kept indoors. Sylvie might simply be thinking about it as if it is a human being.

This was the kind of problem raised at the Animal Welfare Assessment Contest held in the US last November. Teams had to decide whether tortoises were better off in a zoo with toys to play with or in the desert where they naturally live.

One team argued that they were better off in the zoo. They would be protected from danger and enjoy their toys. But the judges said wild animals can only thrive away from humans.

But are thriving and being happy the same thing? The philosopherA thinker who comes up with ideas about big questions in life. Thomas Nagel says we can never tell what animals are feeling.

Others say we can, by watching them. We can see what they choose to do and how they react in different situations. It is easy to tell when an animal is frightened, since it will freeze, run or shy away from danger.

A group of scientists recently used AIA computer programme that has been designed to think.  to try to interpretExplain or decide on the meaning of something. the grunts of pigs. They claimed that they could accurately tell what the animals were feeling 92% of the time.¹

Other researchers have worked on animals' facial expressions. They say that you can measure fear or pain by changes in ear positions or how much they show the whites of their eyes. Some animals, though, tend not to show such emotions in case it encourages predatorsAnimals that prey on and eat other animals. to attack them.

Measuring an animal's heartbeat is another way. As with humans, an increased heart rate shows it is suffering fear or stress. Levels of hormonesChemicals created inside living creatures. They are used to send messages from one part of the body to another. such as adrenalineA hormone made by the body in response to a stressful or threatening situation. can be used to measure stress.

Can we know what animals are feeling?

Yes: It is easy to see when they are scared or angry or depressed. What we can observe for ourselves is now being backed up by biological measurements and analysis aided by AI.

No: We are always tempted to anthropomorphiseAttribute human characteristics to something which is not human., but we know very little about how animals' minds work. As Thomas Nagel says, they are so different that comparing their experience to ours makes no sense.

Or... We can tell when they are frightened or stressed, because that is directly reflected in their behaviour. It is much harder to tell if they are happy, or even if they know what happiness is.

Philosopher - A thinker who comes up with ideas about big questions in life.

AI - A computer programme that has been designed to think. 

Interpret - Explain or decide on the meaning of something.

Predators - Animals that prey on and eat other animals.

Hormones - Chemicals created inside living creatures. They are used to send messages from one part of the body to another.

Adrenaline - A hormone made by the body in response to a stressful or threatening situation.

Anthropomorphise - Attribute human characteristics to something which is not human.