To find an easy place to pick up this achievement is the level 'Bad Blood'. From the very start almost there is a cut-scene where a raptor (or rather pack of raptors) maul you. If you do this you get 1 free one and I was able to pick up 1-3 more each time before the computer killed them all off. Make sure you 'save' each time before reloading chapter. Not sure where checkpoint kicks in I believe there are 4 raptors I always used the first 3 and saved/reloaded before the 4th died. Took about 15 mins to get this one done from start to finish.