There are three basic reasons why a snake will yawn under normal conditions. To realign the jaw after feeding (as mentioned), to loosen the skin on the head when coming up to slough and to stretch muscles and ligaments that have not been used for a while (similar to us stretching). If a snake is yawning several times an hour this would indicate there was something wrong, such as irritation in the mouth as a result of canker (stomatitis) or difficulty in breathing as a result of respiratory infection. At this stage it does not sound like the yawning is anything to be concerned about.
The question is, why did it miss striking these last two times and why was it so reactive? It doesn’t sound like its coming up to slough – timing and its still eating. So given its eyesight is not the problem, something else was likely affecting it when you went to feed it the first time it missed. I would be looking for a change in environment. Check your temps and the viv. Make sure it’s not mites. Go through any changes you can think of between the feed before and the first feed it missed its strike – new pets, pet suddenly taking greater interest in snake cage, moved cage, new TV or sound system, moved a fridge or freezer nearby (the compressors are noisy), construction going on outside, using an air freshener or toilet deodorant, using a new brand of highly scented soap, kids have been showing their mates the snake, etc. Have you changed your routine with it? Feeding at a different time? Did you source the food item form somewhere different? Did you prepare it differently? ETC
The snake appears to be feeling insecure at the moment which is why it is reacting to your visual presence in the manner it is. Try covering half of the front of the cage with a towel. If it is still reacting, cover more. Keep your contact with it for the next week at least to a bare minimum. That means no handling because that is only likely to stress it out more. Give it a chance to regain its feeling of security. After a week or so, star winding back the towel, a little at a time every 2 or 3 days. Play it by ear, until it can be uncovered completely without going into defence mode. Then give it another week before you attempt to handle it and keep that to once a week for a little while. Basically take baby steps to allow it to regain its confidence in its surroundings.
I would continue to keep an eye out for any signs of sickness at the same time because that can’t be entirely ruled out as the reason for the behavioural change. Secondly, you may find it easier and less stressful on the snake to leave the food item in the cage for it rather than hold it in front of it. If you are concerned about possible ingestion of substrate, or mess, simply place sheet of newspaper folded in four on the floor of the cage and place the rodent in the middle. Develop a consistent feeding routine if you haven’t already. Always feed at the same time, preferably after dark, when they would normally be out hunting for tucker. Never take out and / or handle at this time. You can even introduce food from one side of the enclosure and do your maintenance and snake removal from the other. Eventually the snake will recognise the difference.
If you do have to remove the snake while it is in a defensive mood, open the enclosure and let start making its own way out. Once the head and neck are clear you can use a small snake hook to gently prevent the head from reaching back in if it tries. This way you place your other hand in and lift out the body without fear of being bitten. You can continue to use the hook to gently restrain the head if you feel the need but usually you don’t need to. Basically the hook shouldn’t be bearing any weight. If you need to re-build your confidence, you can wear leather or heavy rubber gloves. I personally don’t believe that allowing a snake to tag you is good for the snake. Besides which, I have a strange aversion for pain!
Bear in mind there is more than one way to skin a cat. This is merely one way to tackle the problem but I have attempted to explain why I think it is preferable.
Blue