Similar to Henry's view of the fighting troops, what contemporary animals have been tossed into a pit for a death struggle?

There arn't any specific animals here.A dog is menrtioned but I think Crane was just going for the men's animal instict to survive,

"To the youth the fighters resembled animals tossed for a death struggle into a dark pit. There was a sensation that he and his fellows, at bay, were pushing back, always pushing fierce onslaughts of creatures who were slippery. Their beams of crimson seemed to get no purchase upon the bodies of their foes; the latter seemed to evade them with ease, and come through, between, around, and about with unopposed skill. "

Wildcats are also thrown in as well as a kitten,

"By heavens, if I had ten thousand wild cats like you I could tear th' stomach outa this war in less'n a week!" He puffed out his chest with large dignity as he said it. "