He could sense that Miss Brocklehurst wasn't thrilled at the thought of going into the Forbidden Forest. Truth be told, neither was he, but he at least was prepared for things he knew were inside the Forest and had a litany of spells to help along the way that Miss Brocklehurst might not.
Harold watched as she picked a feather off one of the brambles and suggesting it might be her owl's. Not the right pattern or size for Bubo's, though. Then there was a screech - and Miss Brocklehurst said something before shooting off into the Forest proper.
Oh, Merlin, he thought. "Miss Brocklehurst, please come back!" But even as he called, he suspected it would do no good - the fear of her dear owl being injured was too strong for her to ignore, it seemed.
Harold made sure to take one of the feathers, studying it for just a moment. Definitely not one of Bubo's, he noted, then sent up a shower of blue and bronze sparks to alert anyone who might be passing, before making a beeline after her - assuming he found Avie, he could always cast a quick Avenseguim to track the feathered friend once he knew that she was safe, that had to be his priority.
While it was approaching twilight outside the forest, the haze of the canopy left a more menacing, darker look to what was left of the day. He stopped, trying to get his bearings, and cast a quick Lumos to get some light. It wasn't entirely a welcome move within the Forest; many things dwelt there that preferred the darkness and especially detested uncanny brightness.
"Miss Brocklehurst!" he called, "Avie! Where are you?" Unfortunately he only had a feather from her owl, not anything of hers, so tracking her was a little more difficult. Harold stopped, seemingly at a small clearing in between clumps of trees, and no way to know where Avie had gone.
"Oh, Merlin," his voice said, rather unconsciously. Holding his wand in his right hand, his left hand's fingers started doing some odd gesture, like he was turning pages, except no book, no pages. "Aha, yes!" The spell he had been thinking of sprang into focus in his mind.
With a deft wave of his illuminated wand, he spoke with a stern, authoritative voice, much more so than his usual teaching tone, while fixing the image of Avie Brocklehurst in his mind. "Homenum Revelio!" He hoped Miss Brocklehurst would not be too distressed by the sensation, but he needed to find her - urgently.
A marker appeared in his field of vision - to the left, and off he went, calling for Avie as he did. There was another screech, it seemed to be in the direction he was headed, briskly at that.