Tipping his head to the side, Sirius waited to see if his request would be clear enough for the other wizard, thankful that it was. His actions were already borderline suspicious and Sirius had no way of knowing who, exactly, he was dealing with or how long it would take for them to become skeptical that he was just a dog. Of course, Sirius couldn't deny that he was being far too reckless to maintain his secret for much longer, and he endeavoured to attempt and convince himself to be a tad more responsible, for his sake and for Remus's.
Sirius barked playfully in thanks, snatching up the piece of toast and chomping away at it. He was nearly about to relax when he saw a wand produced and was almost entirely certain he had been found out. Assessing the room for exits, his mind was racing, thinking about nothing other than escaping. Later, when he was no longer a dog, that feeling would be complicated, regret and anger, all turned in onto himself, would take over, winding around the panic to drag him further down.
But the spell he expected never made contact, instead, an entire plate of food and a bowl of water were suddenly set in front of him and Sirius felt a great deal of stress seep out of his body. From all his years at Azkaban, with his very name inspiring nothing but malice and disgust, Sirius had forgotten about the kindness of others and was only just beginning to relearn it. Cautiously, Sirius crept closer to the food laid out on the floor and once he was certain it was safe, ravenously devoured the lot, water going everywhere with how fast he was drinking it. For a moment, his pride didn't get in his way and Sirius didn't think of it.
Once he was done eating, Sirius lifted his paw up as if attempting to shake hands, the closest he could manage for a thank you in his Animagus form.