On the left side - Gewehr/Kar98k side.

When you have opened upstairs, if a zombie is coming downstairs, walk into the grenade icon under the stairs and then move towards the far end of the hall (power can be off still) and turn and watch the zombie.

He will come down the stairs and then get dragged backwards towards the grenades

Once there, he will 'reset' and come after you.

It is good to know if you are doing the BB multigun glitch and have empty hands.

It is similar to the BB/MP40 glitch by the double tap machine.

On the Verruckt and Shi No Numa maps I have occasionally seen zombies run to a wall gun or to the box after you buy an item from it, I assume this is similar and may be further exploitable.