When Daniel Kish clicks his tongue, the world answers back.
Cars, trees, doorways, bollards on the pavement… all are identified and mapped in his brain using information gleaned from a series of sharp little taps of his tongue against the roof of his mouth, two or three times a second.
From an early age, the Californian developed a sonar technique which allowed him to navigate using echoes from repeated tongue-clicks. The skill has led to him being dubbed a "real-life Batman" - a description he welcomes.
"It is the same process bats use," he says. "You send out a sound or a call and sound waves are physical waves - they bounce back from physical surfaces.
"So if a person is clicking and they're listening to surfaces around them they do get an instantaneous sense of the positioning of these surfaces."
The echoes from his clicks inform Kish about an object's distance, size, texture and density. It's enough for him to differentiate between, say, a metal fence and a wooden fence.