Firstly, your hypothetical legion is actually reacting in a way to prevent death. Secondly, if we were to continue killing the legionnaires without them having

Firstly, your hypothetical legion is actually reacting in a way to prevent death. Secondly, if we were to continue killing the legionnaires without them having any success against us they will either retreat or break. I'm not certain of the sources of cows, bison, and whales reactions to their herd being killed; but taking the reactions as stated would certainly give pause for thought on gence. Markers of intelligence include awareness of the self, awareness of others in relation to the self, awareness of death. To not react to the murder of another member of your herd either requires a lack of fear of death, or a lack of one or more of tgose aforementioned markers of intelligence.