Nybbles == 4-bits, so looking at the byte values in decimal doesn't show it.

Look at the patterns of the nybbles (in hex):

## 'b' lists bits lsb->msb 
print unpack 'b*', "\x12\x34";;

1248 1248 1248 1248
0100 1000 0010 1100
   2    1    4    3

## 'B' lists bits msb <- lsb
print unpack 'B*', "\x12\x34";;

8421 8421 8421 8421
0001 0010 0011 0100
   1    2    3    4
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