Fenrir shook the hand he'd just severe until the wand slipped free then he flopped onto of the gasping Auror as he crunched the limb and swallowed it. he didn't expect the man to go still then lurch upwards as much as he could, dislodging Fenrir from his position and sending him rolling away. Nor did he expect the Auror to lunge after his wand and hold it so expertly in his left hand.
Fenrir growled and leapt at the Auror just as he cast a spell. He grunted when the spell hit him and knocked him backwards, rolling onto his feet as quickly as he could. He deliberately hunched over and whimpered, though the spell... a stunner, if he was any judge... had not had quite the effect the Auror probably hoped for. He saw the man eye him warily, his injured arm held close to his body. It seemed he had taken the opportunity to cast a quick spell to bandage it though the bandage was rapidly turning red.
He waited, still hunched and whimpering, until the Auror had taken a tentative step forward then he burst into action. He launched himself at the Auror, hitting him in the chest and bearing him to the ground. He snapped at the man's wand, snapping it in two then lunged forward and closed his jaws around the man's throat.
He closed his jaws but didn't rip the man's throat out. His teeth punctured the man's skin but instead of continuing with the action, he kept his jaws how they were, cutting off the man's supply of air. It didn't take long for the man to start struggling, grabbing at Fenrir's fur, yanking on it and punching him. Finally the Auror convulsed and Fenrir was forced to adjust his position to go with the convulsions and keep his grip on the man's throat.
The man eventually jerked violently and went still. Fenrir held onto his throat for a little longer until he was certain the man was dead then he let go and whirled around to see how Natasha was handling the woman.