Definition Request: What is "Observer Contamination

[RAD4921]

I am looking for a definition. I know the word but I forgot it. This topic came up when a friend of mine were talking today.
What is it called when an outsider comes into a primitive society (or observing a pride of lions, ect) and the presence of the observers contaminates the environment they are trying to capture "naturally"?
Thanks Rad

 

[Hurkyl]

The observer effect?

 

[Gokul43201]

second that