@Void-the_bat That can be accessed via a cheat code where Jim is given a mask or wig pasted over his head. The DK mask was the developer's middle finger towards the use of prerendered CGI in that game and how much it beat EWJ in sales.

On a related note, the PC version (Windows not DOS) has an exclusive and very secret idle animation where Jim takes a piss break with his back viewing the camera, looking back to see if the player is still there. It's confirmed the animation can be triggered via F10 as revealed in the comments for this video demonstrating it: [LINK]

In the Windows port for Pitfall: The Mayan Adventure, Pitfall Harry Jr. has a similar idle animation and it can be triggered the same way
The animation can happen in the games, but it only happens on very rare occasions

So is nobody gonna point out the Donkey Kong mask?