Thanos smiles darkly as he puts pressure down onto Loki's throat, lifting him up with one hand that is currently strangling him just after receiving the tesseract, but he did expect Loki to try something. Going straight for the throat was pointless and stupid, but a bold move. One that will result in his death which Thanos is more than happy to carry out. However, one thing he never expected, the last thing he expected, was for a sparkling dimension portal to open up in the room and for Doctor Stephen Strange to step out of it, Thanos recognising him instantly as does Loki.
He'd know his boyfriend anywhere. They met back on Misgard as the wizard had him falling for thirty minutes in an endless fall. When he was finally released from that hell, Loki instantly drew out his knives to attack Stephen, but was thrown through a portal instead. They dated shortly after when Stephen paid him several visits on Sakaar to "keep him in check", but it was obvious to the both of them that there was something between them: a spark, and not the magic portal kind that Stephen can conjure up out of thin air just as he's done now to appear here, much to Thanos' confusion. Stephen takes one look of the situation before looking directly at Thanos.
"Thanos, I've come to bargain."
Thanos narrows his eyes at the wizard and sighs out as if it's painful to hear those words.
"Dormammu warmed me about you."