Animal behaviour experts are launching a study into why cats sometimes bite their owners when stroked.
Researchers at the University of Lincoln say petting aggression is a common problem, with more than 20% of household cats showing it.
They are looking for cat owners who have experienced aggressive behaviour from their pets to video their experiences for the study.
Theories for aggression include boredom or the need to reassert control.
Professor Daniel Mills said: "Many owners are bitten or threatened by their cats when they play with them or when they are stroking them.
"There are many theories as to why so-called 'petting aggression' occurs.
"It could be a sign that the cat is simply getting fed up with the owner, or it could be a response to the ecstasy of being stroked, or it could be the cat trying to assert control.
"The truth is that we simply don't know the reason for this behaviour.
"The aim of this study is to look more closely at exactly when such aggression occurs so that we can help prevent it and treat it more effectively."
He said his team wanted to gather video evidence of cats attacking owners.
"We want to see occasions when it does as well as when it does not happen," he said.