In Photos: National Puppy Day

The popularity of squash-faced breeds like this pug has soared in recent years, prompting the British Veterinary Association to launch the #breedtobreathe campaign earlier this year to highlight the health problems that pugs suffer.

Photograph: Alamy

Puppies all over the world are trained to be sniffer dogs, with prominent uses including searching for drugs and explosives. However, a study in the Animal Cognition journal in 2011 suggested that sniffer dogs are often responding to visual cues from their handlers that someone or something is suspicious. In controlled experiments, dogs would identify an area to search for drugs if their handler had been told drugs were there, even if there was nothing to find.

Photograph: William West/AFP/Getty Images