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.
AI - A computer programme that has been designed to think.
Interpret - Explain or decide on the meaning of something.
Claimed - Said something is true, often without clear evidence.
Stress - Feelings of worry or pressure.