The Lynx Chip's Challenge, unlike the MS version, will read two keys held simultaneously in the process of running as running in the first direction pressed. The second direction is a subordinate keystroke, which will take effect only in two situations. The first situation is that when during (not at the beginning of) a straight run, the primary keystroke becomes illegal but the secondary keystroke is legal, they will reverse priority and Chip will move in the previously subordinate direction. If, however, there is a block in the subordinate direction, block slapping takes effect.
When the subordinate direction is pressed after Chip starts moving in the primary direction, but before the block's row or column is reached as the case may be, the block in question will be moved one space in the subordinate direction, as if it had been flicked. Therefore, if the player is fast enough, a block one row or column away can be slapped.
In this cut from Zartacla, using Lynx rules, Chip can get block 2 off the fire space without being killed, and therefore exit the level in a total of five seconds. Chip would come onto [10, 0] playing through the level as normal, and when he moves D, within half a move the L key is also hit. The combination of this is such that when Chip moves 2D, block 2 moves L, such that block 3 or 1 links to its dirt and Chip can exit the level. Note that if the exit and hidden fire were on row 1 in the above diagram, and there was a wall above [10, 0], this would be impossible to do. However, block slapping could be performed by running vertically instead.
Why it happens
It is likely that block slapping is an ancestor of the coding which allowed for the Mouse Panel Glitch. Both behaviors involve an attempted move in one direction, such that another direction entirely is moved. Since the flick is not possible in Lynx, block slapping is its closest relative.
In the original Lynx game
Block slapping in the original Atari Lynx version of Chip's Challenge is more flexible than in Tile World's emulation. Someone more knowledgeable in the matter should expand this section.
In Chip's Challenge 2
In Chip's Challenge 2, whether or not a block can be slapped depends on the tile that is underneath. If Chip or Melinda could enter the tile normally if there was no block, the block can be slapped; otherwise, slapping is impossible. For example, Melinda could not slap a block on gravel unless she has hiking boots, Chip could not slap a block on a female-only sign, and neither Chip nor Melinda could slap a block off a lock unless they have the appropriate key.
In some situations, it is also possible to slap a block while moving only two tiles. Once again, someone more knowledgeable in the matter should expand this section.
A variation of block slapping in Chip's Challenge 2 is wall slapping. If Chip or Melinda moves past a series of walls while holding a second key in their direction, the wall will be slapped. This can reveal hidden walls and invisible walls, clear fake blue walls and expose real ones, and apply steel foil to walls.
A deadly variation occurs when holding a second key while walking past a monster. If Chip or Melinda does this without a helmet, they will instantly die and have to start the level over.
In official levels
Block slapping is required to solve Two Sets of Rules when playing in Lynx. It is also required to solve several Lynx-only levels in CCLXP2. In addition to this, several other official levels, including Zartacla and Reticulating Splines, are busted due to block slapping.