Thanos flicked his ear instinctively when he heard a faint snarl and, realizing it was a sign that he had noticed Portal (because, really, who else could have made the sound?), quickly pawed at it, making it look as if it flicked because it tickled. He sniffed lightly. It was hard to ignore someone when it was done on purpose.

"Wanna tell me what it is?" he cooed playfully, having no idea what kind of effect his actions were having on Portal. He scratched the dragon's chin, wondering if it was ticklish.