Dogs tilt their heads when you speak to them to better pinpoint familiar words. Your dog is tilting its head when you speak to it to pinpoint where noises are coming from more quickly. This is done to listen out more accurately for familiar words such as 'walkies' and helps them to better understand the tone of your voice. If a dog doesn't tilt its head that often (as those with shorter muzzles might), it's because it relies less on sound and more on sight.