If you are a cat owner, you have probably noticed that your feline friends like sleeping next to you at night (and, if you're lucky – not playing with your toes). However, they do this not only because they like you – feline experts believe there are plenty of reasons for cats to sleep next to humans.

If an unfamiliar voice speaks to you when you sleep, it can "set off an alarm", as our brains remain alert to any possible threats coming from strangers, research suggests.