Ajahn Brahm stated that he ate snakes and frogs during his training, does this mean that it is acceptable to kill animals?

Not to kill animals is the 61st pattimokkha infraction, in the section called paccittiya, rules entailing confession. Thus, until the monastic confesses his infraction the sangha is tainted. Confession alone is sufficient to expiate the infraction.

i know a method monks in thai forest tradition would do. Monks would sun (or air) dry plain rice received from alms round and then soak it in water when ready to eat. Vinaya (monastic codes) allows monks to keep food for certain period. PS. Snake is one of 10 meats not allowed for monks. I think it might have a context to it when ajahn Brahm said he ate one.

That is right, also for you, there is not fault is simply eating. There is no unwholsesome deed with eating meet. It would be of course unwholesome to kill, or to tell someone to kill or being happy or approve the killing. As for a monk, he would not be allowed to eat certain kind of meat, so for example snakes. A Bhikkhu would also not allowed to accept raw meet. So in relation of those questions, you would need to ask him further. Maybe they found corpse and used them for their nourishment.

Once more, for a Bhikkhu, if seen, heard or assumed, that a living being was killed for his nourishment, he is not allowed to eat it.

As for killing (by body, speech or though - in being happy about it), all of them are unwholseome deeds, what ever reason and for whom ever. As for breaking the precepts formal, only bodily actions or verbal actions who cause end effect the death of a living being, are a fault at least.

As for the frog story (just saw Upasaka Chris added the article). Its very usual under framers in SOAsia to eat frogs. They are prepared in various ways. Having lived in a small remote forests village in northern Cambodia as an Anagarika for a while, it happened often that villager came and gave frogs as a alms donation. Honestly Atma was not able to eat them having be boiled, although he has rarely a problem with any kind of food. They are like balloons (if you know the Shrek cartoon). How ever, with time, when people find out that you are not seeking pleasure in this or that kind of food they will naturally avoid to give such, not to speak of even kill that they are able to give. Alms are shares of what one has. Its seldom really Dana if it is taken for the purpose to give.

Ajahn Brahm is a British Theravada Buddhist monk, and a disciple of the Gautama Supreme Buddha. This this issue is of no concern to him. He knows very well that his master, The Supreme Buddha did not encourage us to eat meat or become vegetarians. The choice is entirely up to us. The important point is to take to heart the Buddha’s guidelines in MN 55 on the three conditions for unallowed and allowed meat.

A monk is not allowed to cook and has to be totally dependent on the offerings of lay supporters. He is also taught that he should be easily supported and looked after. Since he is not allowed to ask for any preferential food (except during sickness), a monk cannot choose his food. He has to accept what is being offered. Lay people have more freedom to choose their food, and for lay people it is entirely up to individual preferences when it comes to eating meat or becoming a vegetarian.

So it is very beneficial for those who want to walk this path to its conclusion, not to be too critical of others no matter what our preferences are. The most effective way to reduce the killing and cruelty in the world is for people to understand the Buddha’s teaching. Ultimately, suffering (dukkha) is a characteristic of life, and the way to end suffering is to practise the Noble Eightfold Path of the Buddha to get out of the rounds of rebirths.

Killing for any reason is a serious offence for both monks and lay people. Monks can't cure or cook food. They are allowed only to reheat already cooked food. They are not allowed to eat uncooked flesh or fish.

Here's an extract from an article by Ajahn Brahm, What the Buddha Said About Eating Meat,

Towards the end of the Buddha's life, his cousin Devadatta attempted to usurp the leadership of the Order of monks. In order to win support from other monks, Devadatta tried to be more strict than the Buddha and show Him up as indulgent. Devadatta proposed to the Buddha that all the monks should henceforth be vegetarians.The Buddha refused and repeated once again the regulation that he had established years before, that monks and nuns may eat fish or meat as long as it is not from an animal whose meat is specifically forbidden, and as long as they had no reason to believe that the animal was slaughtered specifically for them.

The Vinaya, then, is quite clear on this matter. Monks and nuns may eat meat. Even the Buddha ate meat. Unfortunately, meat eating is often seen by westerners as an indulgence on the part of the monks. Nothing could be further from the truth - I was a strict vegetarian for three years before I became a monk. In my first years as a monk in North-East Thailand, when I bravely faced many a meal of sticky rice and boiled frog (the whole body bones and all), or rubbery snails, red-ant curry or fried grasshoppers - I would have given ANYTHING to be a vegetarian again! On my first Christmas in N.E. Thailand an American came to visit the monastery a week or so before the 25th. It seemed too good to be true, he had a turkey farm and yes, he quickly understood how we lived and promised us a turkey for Christmas. He said that he would choose a nice fat one especially for us... and my heart sank. We cannot accept meat knowing it was killed especially for monks. We refused his offer. So I had to settle for part of the villager's meal - frogs again.

Monks may not exercise choice when it comes to food and that is much harder than being a vegetarian. Nonetheless, we may encourage vegetarianism and if our lay supporters brought only vegetarian food and no meat, well... monks may not complain either!

May you take the hint and be kind to animals.

My understanding therefore is that "frogs" is what the villagers shared, as alms.

Wikipedia's Thai Forest Tradition article talks of a morning alms round (and not of monks catching animals and killing them and cooking their own food).

Other Google search results say things like, "Thai forest tradition monks cannot handle money or cultivate, cook or store ...", and "The monk does not store or cook food but daily enters the nearby village ...".