On the one hand, he's had to deal with illusion-Arabella a lot during his stay in the carnival. On the other hand, Strange has a one-track mind that's always planted towards his wife.

"Stay put," he'll tell Ignatius. "There's something here."

Veeeery tentatively, he walks over towards where he thinks Arabella's voice is coming from, muttering a spell-breaking incantation under his breath as he does so. He doesn't exactly know what magic (if anything) he's breaking so who knows if the spell-breaking actually works. But he's just going to be a little cautious while he goes right up to investigate the thing.