In the manga, the does not actually swallow Gon and Killua.
Episode 5 of the Hunter x Hunter 2011 anime, titled , primarily focuses on the hazardous journey through the Milsy Wetlands (Swindlers' Swamp) and Hisoka’s brutal "test" of the applicants. Key Plot Events Hunter X Hunter 2011 Episode 5
The in the swamp do not explode in this anime version, unlike in other depictions. Production Note: "TV vs. Home Release" In the manga, the does not actually swallow Gon and Killua