I feel like you're overthinking this, guys. He didn't have 1v1 UFC fight with his victims. He went with a combat knife while they slept and were tired and possibly drunk, as well. He also had the element of surprise. It really wouldn't take that much effort, if we're being honest, especially considering that the only person who would a physical match would be Ethan. . He held virtually every possible advantage he could have over his victims. Is it a risky attack? Yes, it absolutely is. But it really didn't require all that great physical strength or anything. Furthermore, a Ka-Bar (or something similar) isn't some pocket knife, it's purposefully designed to kill.