'hen' indicates a direction. 'imod' can be used in more contexts, e.g. as 'against' or 'opposed to', but can also be used in the example above
The fact henimod is written together is actually a trap as it seems to be pronounced as a different word from imod and almost attatched to the verb. Is this just me or is that the right pronounciation?
I hear: Vi løberhen imod fuglene