When the animals are let loose and a stampede breaks out in the menagerie of the Benzini Brothers circus, workers, performers, and animals run in all directions. Jacob sees Leo and one of the kitchen workers under the kitchen sink, shivering in fear.  Leo is one of the big cats at this circus.  This may be confirmed by one of Jacob's lines in which he says that he saw "man and beast" under the sink.  The reader assumes that the man is the kitchen worker, so the beast must be Leo.  The scene is a bit ironic, especially since Jacob has previously had a bad encounter with one of the big cats--Rex, one of the lions, nearly bit his arm off.  So, here it is ironic that one of the big cats and a man are stuffed under the sink together.