Mortimer struggled a bit, then stopped when he was told that the rest of the Lestranges had it also. His eyes went wide. If they had it, the the whole town possibly did. And as a Healer, he was curious as to why.
When he mentioned Bellatrix dealing with him, his blood ran cold, nodding at Rabastan's demand. He pulled his wand and a clear vial, filling it almost to the top with Rabastan's blood. He capped the vial as Rabastan let go.
"I will work on this at once," he said. Thankfully, Rabastan merely nodded, allowing him to Apparate back to his lab.