Can we know what animals are feeling? Scientists are looking at clever ways of exploring how other creatures feel. Some say it could change the way to treat them.
The quest to know what makes a tortoise happy
Sedate: The Sonoran desert tortoise (above) plods its range, browsing wildflowers, scrub grasses and cactus. Glossary
Frustrated - Annoyed or upset, especially because you cannot change something.
Veterinary - Relating to treating sick animals.
Desert - Dry land where there is very little rain and few plants.
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.
Stress - Feelings of worry or pressure.