Word Squares
Circleellipse paradox 
In each of the following squares each letter appears twice, and each pair of rows has one letter in common.
Examples (in the first square): letter T is in rows 3 and 4; letter A is in row 2, twice.
English word square  Latin word square  5 x 6 version 
B I B L E

M U T U S

L O V E L Y

Either of the above can be used as the basis of a very simple card trick. Collect 10 pairs (e.g. black 2s, red 9s, or whatever). Place them down apparently at random, but in fact in pairs marked by the letters (you could start with the two Ls, say, then the two Hs, and soon). Ask the observer to select a card, and you can immediately select its mate  hopefully to the amazement of the observer.  This took me 20 minutes, one mad day  I'd never manage it again! Can you construct a 6 x 7 version? Some can be found on the internet, but the ones I've seen include at least one very unsatisfactory word. 