I found this site by accident. The expression, 'no room to swing a cat' does indeed come from the sea faring days and there being insufficient room except on the quarter deck, with the crew assembled on the main deck for a flogging to take place. It is, however, NOT associated with 'letting the cat out of the bag'-meaning to discover a secret or uncover a ruse. This comes from when piglets were sold in sacks. Unscupulous (though enterprising) farmers would place a cat in the sack and attempt to sell it at market as a pig. A canny buyer would open the sack to discover, not a pig but a cat, hence letting it out of the bag. This is liked to 'buying a pig in a poke' (sack).