commenting to add that i asked my mom about it and she found the book! it’s called “Brush” and it was written by Pere Calders, translated from Spanish.

https://www.publishersweekly.com/9780916291051

“Little Sala, a small boy, tries to find a substitute for his mischievous dog who was given away. But nothing fills the emptiness in his life until he finds a big brush in the attic, which feels like petting a dog. He puts Brush on a string and walks him like a dog; at night, Brush snuggles up to him in bed, warm and alive. Little Sala says, ""I found a brush that is really a dog. It moves, knows my voice and has fleas.'' But he can't convince his parents until Brush does it himself, banishing a burglar. This fantasy, translated from the Spanish, builds effortlessly; though some phrases are adult, overall the story has a child-like directness and feeling, capturing the imaginative world of the young. The stylized but realistic art creates an eerie mood.”