It was fairly obvious too. With all that running and the hyperventilation, Harth's heart should have been racing. When Heero placed his hand on the boy's back, he felt nothing.

Pulling his hand away, he stood up and took a step back. That wasn't right. Harth looked clearly humanoid, so he should of had something like a heart. Everyone besides the vocaloids (that he knew of) had hearts. Why didn't Harth?

"You don't have a heart beat."