Loki was surprised to see that Michael did not hesitate to agree to his conditions, despite Loki saying that he had placed a spell that could kill Michael if he betrayed him. It was a fake spell Loki thought of to intimidate Michael since Loki did not want to teach. Yet Michael did something Loki never expected as he actually accepted.
Loki had planned to keep on rejecting him but seeing the determination in Michael's eyes made it very clear that he would never give up, not to mention that look of determination always reminded him of her. Loki knew he was going to regret doing this, but.
"Fine, as long as you hold on to your end of the deal, I will fulfill mine."
When Michael heard Loki's answer he looked pleasantly surprised. Michael quickly did a martial artist gesture of recognizing a master, but before he could say the words Loki stopped him.