I'm not going to talk theology, but please let me draw your attention to the real difference betwen this account and the one of Mark. It's not about heads or feet - just read the last sentence. What we have here, in my opinion, is an eyewitness account. The detail is the detail an eyewitness would remember. There are many other narrative passages in the Fourth Gospel that support this view, even though conventional biblical scholarship denies it.
And note also that the narrator mentions himself - Lazarus of Bethany.
As others have said, the New Testament was written by fallible men. They agree to an amazing extent on the gospel itself - the "good news" of Jesus - but they often differ on the details.
Note that Luke (vii:28-50) records the same incident, with more detail that is almost certainly interpolated, making of the incident a small Socratic dialogue - very Greek. And he also says "feet".
What I think happened is that somewhere between the event and the Q version, on which both Mark and Matthew are based, somebody decided that anointing the feet didn't make sense, and substituted head - an obvious echo of Ps xxiii. In other words, he was imposing onto the narrative a Jewish perspective, and getting it wrong.
A final question,if I may. Does this inconsistency make you doubt Jesus? After all, the Bible is but a means to an end, and He is that end.
Best wishes.
I don't know if this inconsitency makes me doubt Jesus or not. It does make me question whether or not my original beliefs about the Bible were correct (that it is infallible).