To support the central idea that Snowball is ruthless, the following two key details from the passage are most relevant:
- “No sentimentality, comrade!” cried Snowball from whose wounds the blood was still dripping.
- "War is war. The only good human being is a dead one.”
These lines emphasize Snowball's harsh and uncompromising attitude towards violence and human life, highlighting his ruthlessness in the context of war.