Osamu looked human to some, but there was something off about him.  Besides from his behavior, Seamus saw...imperfections.  these didn't seem natural at all.  But it didn't seem like a robot either.  The Irishman saw nothing more than an abomination that was excreted out of a syringe.  The mutant wasn't even born properly, let alone raised properly.

Seamus was the new arrival, yet even he could see wrongness in all levels about Osamu.  The more he looked onto the vat-grown being, the more he didn't want to see.  This was an affront to the laws of nature!  After Osamu stopped talking, Seamus had to take a minute to recover his composure.  His will to fight was bolstered from a desire to eliminate the mutant once and for all.

"I am not to be bargained with..." Seamus himself was familiar with the use of terror.  Not negotiating with terrorists, the lad curtly shot down the offer and didn't even think that the artificial human would hold up his end.  Turning to the Spanish queen, he said with a roused tone, "We're taking down that shit-from-a-syringe!"

Osamu should not have talked rot.  While Seamus indirectly insulted his own leaders, he had bit of a disdain for artificial humans.  Transhumans and posthumans were one thing to him, but vat-born beings?  That was a horse of a completely different color in his opinion.  God made men, but science made them equal.  It's NOT the other way around!