From Worms Knowledge Base
Herd-doubling glitch (or Cow doubling glitch) is a patched bug in Worms Armageddon which allowed a player to release double the number of mad cows than the selected herd size by jumping and pressing space (or even jumping while holding space, which was easier) after releasing the last cow in the selected herd. All but one of the extra cows released by exploitation of this bug were subtracted from the team's weapon arsenal, but the releasing of cows was not halted by the number of mad cows in the arsenal reaching zero. Also, in the past, a loophole could be exploited through means of message injection. It was possible to set the herd size to 0 or a number above 5, the former allowing the release of an unlimited number of cows, even if the team had only one cow in its weapon arsenal.
Both the herd-doubling glitch and the infinite-herd loophole were closed by Deadcode with the release of version 3.5 Beta 1 on 2002-08-09. However, the glitch can optionally be re-enabled through Extended Scheme Options added in v3.8 Update. Due to keyboard input processing changes, the method for triggering this glitch (when it is enabled) is now different – after the last cow in the selected herd has been released, Space must be pressed at least one frame after pressing the key used to initiate the jump (i.e. Backspace or Enter). Note that this will instantly end the retreat, so if a key-combo jump is to be used (e.g. Backspace twice for a backflip) the full key combo must be finished at least one frame before pressing Space.