What is the ingredient in cat treats that they go frantic for?

Cats love treats for a variety of reasons. As obligate carnivores (i.e. they must eat meat to survive), cats enjoy the taste of animal-based proteins.

Specifically, some cat foods contain compounds such as nepetalactone (found in catnip) and actinidine or dihydroactinidiolide (in silver vine), which can trigger a euphoric or playful response.

It’s thought that the reaction is a response to the stimulation of the opioid receptors in the brain and increased production of endorphins. 

Not all cats are sensitive to these chemicals, as the reaction is genetic; about 60-70 per cent of cats respond to catnip.

Ruth Franklin, Rugeley, Staffs

QUESTION: What is the world’s largest denomination banknote?

Currently, the highest note in circulation is the Singaporean $10,000 note (worth £5,860). 

Although it was discontinued in 2014 by the Monetary Authority of Singapore, it remains legal tender.

There is also the Brunei $10,000 note, which, under a Currency Interchangeability Agreement of 1967, is interchangeable with the Singapore dollar.

The highest denomination banknote ever issued was the Hungarian million billion pengo note (one with 20 zeros), which was printed on June 3, 1946, and withdrawn on July 31. 

After the Second World War, prices in Hungary began to double every 15 hours, causing the country to experience the highest rate of hyperinflation ever recorded.

Mr A. Callaghan, Glasgow

QUESTION: Which is the world’s largest model rail set?

Further to the earlier answer, I visited Miniatur Wunderland in Hamburg with my wife and we were blown away by the incredible displays.

Around the ten-mile track are displays representing different countries: for example, the Grand Canyon and Cape Canaveral appear in the US section.

The attention to detail is staggering. Cars and trains move continuously, bridges and crossing gates rise and fall, or open and shut in tandem. 

Stadiums are full of cheering miniature people, rockets take off, fairground rides go round or up in the air, and cruise ships sail into harbours. 

It’s well worth a visit.

Lyn Pask, Blackwood, Gwent

Tomorrow's questions:

Q: Why was Porter Rockwell dubbed ‘The Destroying Angel of Mormondom’?

Phil Thomas, Leominster, Herefordshire 

Q: Which countries have the lowest female representation in their parliaments?

Claire Edwards, Derby 

Q: What incomplete novels have been completed by other authors? Were any successful?

James Harding, Sutton, Surrey