It's the schnapps--just the plain s- c-h-n-a-p-p-s schnapps.

An' he's a good sailor-man, Jerry, when he's sober.

But when he's schnappy he's sheer lunatic.

Then his noddle goes pinwheeling and he's a blighted fool, and he'd snore in a gale and suffer for sleep in a dead calm .-- Jerry, you're just beginning to pad those four little soft feet of yours into the world, so take the advice of one who knows and leave the schnapps alone.

Believe me, Jerry, boy--listen to your father--schnapps will never buy you anything." Whereupon, leaving Jerry on deck to stalk the wild-dog, Captain Van Horn went below into the tiny stateroom and took a long drink from the very bottle from which Borckman was stealing.
The stalking of the wild-dog became a game, at least to Jerry, who was so made that his heart bore no malice, and who hugely enjoyed it.