I noticed that you can hurt HECUs by throwing a regular grey barrel at them (I don’t know if other objects work) and if you kill him this way, he explodes as if killed by large explosion. This is funny and weird, and should be fixed I don’t know if this works with other enemies.
@EDIT
I got the same effect by killing a vort with a chair (I had to throw it at him like 15 times). That proves that it works for all enemies and all objects.