How can you tell when a bearded dragon is choking?

If they aren't closing their mouth properly, and are struggling to breath and swallow, something's obviously not right. A rubber spatula can be used to open the mouth to look, and tweezers can be used to remove any offending item.

Bearded dragons are not likely to choke on appropriately-sized insects and greens, however. Be certain that insects and greens are no larger than the space between the dragon's eyes. Oversized insects can kill baby dragons--not just through choking, but also because their spinal cord runs perilously close to their intestinal tract, and the large mass of chitin will damage the spinal cord...causing hind limb paralysis, and death.