He used magic to get rid of the cow, but he also got rid of a patch of floor..and wall.
She comes back and sighs, setting the cleaning supplies down
"Well...that's one way to do it."
"Perfect!"
"Yes...but do you mind putting back the floor and wall?"
"I can't do that."
"Ah-ok...well maybe from now on we clean the nonmagical way, alright?"
"Mayyybeee?"
"Yes. No more vanishing walls."
"Ugh, fine."
"Thank you."