Making a Knowledge check
A Knowledge check not only serves to identify the correct creature but also identify it's type. So, a zombie-like construct could be identified as such with a Knowledge (Arcana) check, and an actual undead zombie be identified as such with a Knowledge (Religion) check. This is clarified on this post by James Jacobs (Paizo's Creative Director):
So my thought is this: one roll. You simply declare "I want to figure out what this thing is. I rolled a 14." Then the DM asks what the relevant knowledge bonus is and determines if I know what I'm looking at. If it's, say, an aberration and I didn't bother with ranks in dungeoneering, I get nothing. But if it's an outsider and I have ranks in planes, then I might.
This is how I've always run it, and it works pretty well. Although usually I simply cut to the chase and ask the player to roll whatever the actually required Knowledge check is. This does mean that the player gets a clue as to what the monster's type is... if that's a problem (as in the case of an undead masquerading as a living creature, for example), I'll be more cagey about it, maybe asking them to make the roll and then looking at their sheet or asking them for ALL their knowledge ranks.
So, if you don't want to spoil the surprise, you could either ask for all their knowledge bonuses when making a check or even make the check instead of the player. Personally, I prefer to keep notes of the PC's knowledge bonuses and when they make a check, I simply compare that to those bonuses (which is a pain when they are skill monkeys).
Unless, of course, the creature has a special ability to ruse it's identity. Such as mimicking an object or another creature using Disguise. In that case, first, you must see through the disguise (Perception) before you can make the proper knowledge check. Otherwise, you might identify the creature incorrectly and believe in the disguise.