The Mystery of Mr. Balder

Mr. Balder — an excellent cook, virtuoso musician, and lover of reading in solitude. On Mondays, Wednesdays, Fridays, and Sundays, he prepared salmon cutlets with a salmon roe sauce, and on other days — beef fillet with baked potatoes and mushroom sauce. But one day — Thursday — Mr. Balder didn't like, so on Thursdays he mowed the lawn. But one day, when Mr. Balder, as usual, was having oatmeal, a strange advertisement caught his eye:

Tired of mowing the grass?
Get  sheep!
Not expensive