Hard boil the eggs and then rinse with cold water. Peel and chop finely. Also finely chop the beef tongue and pickles. Put the sour cream in a bowl and mix well with the mustard. Wash the chives, drain well and cut into small rolls. Add beef tongue, eggs and cucumber to the bowl and mix everything together well. Season with salt. Stir in all but a tablespoon of the chives as well.