We were driving in the car recently and my son asks, "what would happen if snake came out of your mouth every time you burped?"

I think a normal parent would have reacted much differently than I did.

"What kind of snake?" I ask.

"Well, if you burp once, a spitting cobra comes out. If you burp twice, a king cobra comes out."

"What happens with the cobras when they are out?"

"The cobras will do whatever you say or just follow you around for a while."

"If you burp a lot, do you get a lot of cobras?

"No, you can only get three cobras no matter how many times you burp."

"What if I burp three times?"

"Nothing. One burp is a spitting cobra, two burps are a king cobra."

Thus we have the belching snakes spell for Swords & Wizardry or your favorite retro-clone.

Belching Snakes

Spell Level: Cleric, 2rd Level, Druid, 3rd Level
Range: 30 feet (after the snakes appear)
Duration: 1 hour

The caster begins belching loudly in bursts of one or two belches. If the caster belches once, a spitting cobra appears. If the caster makes a two belch burst, a king cobra appears. The snakes follow commands, but wander off at the end of the spell. If killed, they disappear into nothingness.

Spitting Cobra: HD 1; AC 5[14]; Atk 1 bite (1hp); Move 16; Save 17; AL N; CL/XP 3/60; Special: Spit poison, 30' range (Save with +2 bonus to roll or go blind for 2d8 turns).
King Cobra: HD 2; AC 5[14]; Atk 1 bite (2hp + poison); Move 16; Save 16; AL N; CL/XP 4/120; Special: Lethal poison.

Section 1 to 14 of the OGL are here

Section 15 of the OGL for this article:

15. COPYRIGHT NOTICE
Open Game License v 1.0a Copyright 2000, Wizards of the Coast, Inc.
System Reference Document
© 2000-2003, Wizards of the Coast, Inc.; Authors Jonathan Tweet, Monte Cook, Skip Williams, Rich Baker, Andy Collins, David Noonan, Rich Redman, Bruce R. Cordell, John D. Rateliff, Thomas Reid, James Wyatt, based on original material by E. Gary Gygax and Dave Arneson
Swords & Wizardry Core Rules
, © 2008, Matthew J. Finch
Monster Compendium: 0e, © 2008, Matthew J. Finch
Pathfinder RPG Bestiary, © 2009, Paizo Publishing, LLC; Author:
Jason Bulmahn, based on material by Jonathan Tweet, Monte Cook, and
Skip Williams.
Pathfinder Roleplaying Game Bestiary 2, © 2010, Paizo Publishing,
LLC; Authors Wolfgang Baur, Jason Bulmahn, Adam Daigle, Graeme
Davis, Crystal Frasier, Joshua J. Frost, Tim Hitchcock, Brandon Hodge,
James Jacobs, Steve Kenson, Hal MacLean, Martin Mason, Rob
McCreary, Erik Mona, Jason Nelson, Patrick Renie, Sean K Reynolds,
F. Wesley Schneider, Owen K.C. Stephens, James L. Sutter, Russ Taylor,
and Greg A. Vaughan, based on material by Jonathan Tweet, Monte
Cook, and Skip Williams.
Monstrosities, © 2012, Matthew J. Finch
Swords & Wizardry Complete Rules, © 2008-2012, Matthew J. Finch
Belching Snakes,  ©2015, Sycarion Diversions, Authors John Payne and Jasper Payne