Marine on the right is wearing the Herringbone twill utilities. These were phased out in the 1950s. Semper Fi.

Those toggles are still used to attach the basket to the envelope on a hot air balloon. They permanently attached to one of the ropes and are actually quite difficult to put in and remove from the small eyes in the other rope, no chance of them falling out.

That's what the "wooden dowels" described by BillyB are called. They were in common use to secure blocks to pendants on the ships of the 18th century, and were only gradually replaced by the metal shackles in use for that purpose in today's yachts.
When I first saw diagrams of them I too worried that they could be shaken loose by a luffing sail, or one that was clewed up but not yet furled. But, not having seen the actual object it just can't be they were so vulnerable -- otherwise there would be far more references in nautical literature of tackles letting go unexpectedly.
As recently as 1969, I found a set of signal flags equipped with them on the lower attachment point with a spliced eye on the upper. I can't be sure I used them correctly, having no experienced bosun to teach me, but they did not come undone for me.

This is an interesting tie down system, quick to hook up but prone to failure. The eye of one line passes through the eye of the other and a wooden dowel is inserted. This would be a good system as long as the lines remain tight. As soon as they loosen the dowels could fall out although the way they are turned would prevent this to a degree.

Notice that there are no knots in the ropes. All eyes are formed by weaving the end of the stands back into themselves. A naval practice for years. This interweaving practice was also used to splice parted lines. I still make the eyes this way. Not that hard to do and it looks cooler than a big ugly knot.

Better grip vs. rope burn?