the effect, bit rot the notional cause.

:bit twiddling: /n./ 1. (pejorative) An exercise in tuning (see
{tune}) in which incredible amounts of time and effort go to
produce little noticeable improvement, often with the result that
the code becomes incomprehensible. 2. Aimless small modification
to a program, esp. for some pointless goal. 3. Approx. syn. for
{bit bashing}; esp. used for the act of frobbing the device
control register of a peripheral in an attempt to get it back to a
known state.

:bit-paired keyboard: /n./ obs. (alt. `bit-shift keyboard')
A non-standard keyboard layout that seems to have originated with
the Teletype ASR-33 and remained common for several years on early
computer equipment. The ASR-33 was a mechanical device (see
{EOU}), so the only way to generate the character codes from
keystrokes was by some physical linkage. The design of the ASR-33
assigned each character key a basic pattern that could be modified
by flipping bits if the SHIFT or the CTRL key was pressed. In
order to avoid making the thing more of a Rube Goldberg kluge than
it already was, the design had to group characters that shared the
same basic bit pattern on one key.

Looking at the ASCII chart, we find:

high low bits
bits 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001
010 ! " # $ % & ' ( )
011 0 1 2 3 4 5 6 7 8 9