Yeah, I've been noticing that, and I'm like WTF, why is there no laugh LOL
Maybe my theory would come true though.... MAYBE somehow, his smile DF which was FAILED, awakaned and now he is a TRUE smile user... and we all notice that successful smile users do not have the after effect of laughing...
So maybe that was Oda's way to give Killer his power up for this arc... also do not underestimate smile DFs... Oda could legit give him a sick as design for a nice animal, and it just gets deadly
Like for example, he might legit get an animal in one of his arm that is deadly and poisonous at same time... which would amplify his sword cuts and makes him more dangerous