His pants felt tight at first, muscles straining against the seams. His shirt bunched up in back as a new appendage made its appearance at his rump, unfurling like a small flag, growing in size and fluffiness.

The pants didn't really stand a chance, for his reshaping legs soon could no longer be restrained by the fabric, escaping with a ripping sound leaving his nude from the waist down. That wasn't really a concern for long as the dark fur ran down his back and across the digitigrade legs to his newly formed four toed paws.

Story idea suggested by  skgyae for  RojAdrik . Enjoy!