Toe the line – it’s often written as “tow the line”, but this is incorrect. It is easy to understand where the confusion came from, particularly when the phrase is combined with an entity, as in “toe the company line” or “toe the party line”. It is easy to visualize a poor wretch toiling with the company rope over his shoulder.
The phrase is clearly “toe”, however, and the origin is straightforward. It refers to stepping up and putting your toe on a starting line. It’s related to another phrase, “up to scratch”, discussed below.
“Toe the line” has become corrupted from its original meaning. Now, when you hear of someone “toeing the line”, you tend to think of someone brought to heel (see here for an example), of someone staying within prescribed behaviour, rather than the original meaning of someone stepping up to a challenge. This original sense is still maintained in the phrase “toe the mark”, a more British saying, which retains the feeling of someone preparing for a contest (at least to my ear, it does.)
Up to scratch – The origin of this phrase is related to “toe the line”. In early prizefighting, a mark would be scratched in the dirt, and the fighters would each place a toe on the line, or “scratch”. They would then attempt to drive the opponent off the mark with their fists. Such fighting clearly requires a great deal of physical courage and endurance, and thus it was admirable to be “up to scratch”.
Room to swing a cat – this one puzzled me when I was young. Why would anyone need room to swing a cat? I envisioned someone taking a housecat and swinging it around by the tail. This makes no sense, and is cruel to boot.
I have learned since that the origin is nautical, and refers to the ‘cat’ or ‘cat-o-nine-tails’ with which errant sailors would be flogged. Not having room to swing a cat meant not having room to enforce discipline. And, yes, it’s cruel too.
I need to clarify: in my previous post on words, I said that the I before E rule was a pet peeve. What I meant was that I heartily dislike the I before E rule. I think it a pox and a vexation. English users everywhere should stand up (or, rather, sit down) and reject it wholesale. Why can’t we all just agree that ‘ei’ is pronounced ‘ay’ and ‘ie’ is pronounced ‘ee’?