The only way to know a secret is, is to reveal it or through process of elimination figure out what it is not. There is only 1 card currently to negate secrets, Flare.
In order to use process of elimination you need to know what secrets are out there. Each class has a fixed cost for their secrets, so that will give you no information regarding what it is. The other thing to take into account is the game format and the regularity with which each secret could be expected.
If you are playing Constructed in "Play" mode and your opponent uses 1-2 legendaries on you, it is safe to expect they have access to the rare and epic traps; but if they are playing primarily the basic cards it is more likely they may not have the rarer secrets.
If you are playing Arena, there are certain secrets you see more often than others. For example, most players rate Explosive Trap fairly highly as a Hunter and it is a common.
That said, there is also some basic logic you should use when testing a trap. If you are attacking a hunter, be intentional about which creature you attack with (knowing that the trap could be a freezing trap), this can sometimes be used to your benefit. If the trap does not trigger when you attack, then it is not Misdirection, Freezing, Explosive, or Snake... leaving only Snipe. So then be intentional about which creature you play next. Also, you would want to attack before you play a creature in almost every scenario because of the high probability of Explosive Trap or Misdirection.
3 classes have secrets; Hunter, Mage, & Paladin.
Hunter:
Snake Trap (epic) - trigger: attacking minion, effect: summon 3 1/1 snakes (beasts).
Explosive Trap (common) - trigger: attacking player, effect: deal 2 damage to all enemy Characters (includes you).
Freezing Trap (common) - trigger: any minion attacking, effect: return minion to hand & it costs +2 to play.
Snipe (common) - trigger: "Play" a minion (not "Summon", so for example it does not trigger from paladin/shaman abilities or imp master), effect: deal 4 damage to that minion.
Misdirection (rare) - trigger: When any character attacks a hero, instead he attacks another random character.
Mage:
Ice Block (epic) - trigger: mage takes fatal damage, effect: mage doesn't die this turn, stays at 1 life.
Spellbender (epic) - trigger: target any minion with a spell, effect: randomly select a new target.
Counterspell (rare) - trigger: cast any spell, effect: that spell is countered.
Vaporize (rare) - trigger: attacking player with minion, effect: destroy that minion.
Ice Barrier (common)- trigger: attacking player, effect: mage gains 8 armor.
Mirror Entity (common)- trigger: "Play" a minion, effect: summon a copy (battlecry abilities do not trigger for mage's copy).
Duplicate (common - Naxxramas) - trigger: friendly minion dies, effect: Place 2 copies of destroyed minion in hand
Paladin:
Eye for an Eye (common) - trigger: paladin takes damage, effect: after paladin takes damage the same amount is done to his opponent.
Noble Sacrifice (common) - trigger: attacking anything, effect: paladin summons a 2/1 and your attack is redirected to that.
Redemption (common) - trigger: any of paladin's minions die, effect: return to life with 1 health.
Repentance (common) - trigger: you play a creature, effect: it's health is reduced to 1.
Avenge (common - Naxxramas) - trigger: friendly minion dies, effect: give a random friendly minion +3/+2
This is according to my own experience. I have 257 arena wins and I like to keep stats. I searched previously but couldn't find an official source for this.
1st, 10th, 20th, 30th pick in Arena are always rare or higher: I call this Rare Turn, the others are normal turns.
At any normal turn, you can get one of these sets:
- 3 free
- 2 free 1 common
- 1 free 2 common
- (possibly 3 common as well didn't pay attention, can't verify this)
- 1 Rare turn ( % not sure I would guess about 5% - 10%)
In a normal turn roughly you have a 60% chance of getting a free and 40% chance of getting a common card.
At any rare turn, you can get one of these sets:
- 3 rare
- 3 epic
- 3 legendary
I got a legendary about every 10 games and since we have 4 rare+ picks I assume the chance of getting a legendary in a single rare turn is about 2%
I got an epic about every game so I assume the percentage for that is about 20%
TL;DR:
Normal Turn:
Rare Turn:
- Rare+ : 4 times
- Epic : 20%
- Legendary : 2%
I don't have a source for this its all according to my personal experience. These numbers are most likely wrong, but should give the general idea. More data is needed for better estimates.
In a normal arena deck you will have something like this:
- 15 Free
- 10 Common
- 4 Rare
- 1 Epic/Legendary
Of course if you are lucky you could get 4 legendaries, 10 rares, etc..
Best Answer
Yes, this is consistent and you can use that information to help you play.
For example did the player junk their whole hand at mulligan (less likely to have a killer opening), or keep the whole lot? Did they keep their whole hand but not play it on the first few turns (pieces of a combo maybe)? Did they consider playing a card then play a different one (might that be a spell if they tried to target something first)?
There are programs like Deck Tracker that will do this for you, giving details like which turn they drew it on, whether it came from another card (like duplicate or a discover card), but it is entirely possible to do it all in your head, if you're good at keeping track of things like that.
It can be very powerful to finesse your choice of play, but it's only a little piece of the puzzle, so you still need to think through your turns and consider all possible plays, but it helps to gauge risk.