He didn't yell or scream as whatever-the-purple-light was made his head snap back, but when it stopped hurting and scattering his thoughts, he realized that he'd slumped forward with a groan into Loki's hand round his neck. If he didn't want breathing to become an issue, he needed to pull his head back again.
Then there was the little comment about his venom, and he just grinned. "Spider," he said, as if that explained everything. He would have shrugged if he'd been able to move.