Thank you for your time spent and for the comprehensive review!
During testing, we ran into a problem with the ballista being unsuitable for close combat, so we instructed the zombies to jump onto the ballista slowly in an arcing trajectory. They also reduce their HP to 1 before jumping, just to please the player :)
The bird in the sky was proposed by Veksell (co-author) at the last night before submit to liven up the scenery a bit. She will definitely be glad that you noticed it.