I have animals which took either drug A or drug B (drug factor), and these same animals were either dehydrated or euhydrated (treatment factor).
The F-tests for my ANOVA model tell me that only treatment is significant (drug isn't, and drug*treatment interaction isn't either); but Student–Newman–Keuls (SNK) post-hoc tests show that drug-A-dehydrated is different from drug-B-dehydrated.
Why are the post-hoc tests for this difference significant if only treatment factor is responsible for the differences? Should I change post-hoc? What (different) questions are F test and post-hoc answering?