Below 2.5 ❤ — that is 25 % of your health — you gain Strength I for as long as you stay under the threshold.
The Berserker inverts the soup reflex: drinking your soup costs you your bonus. Played well, it means deliberately staying low to finish an opponent before he finishes you. Played badly, it means dying on half a heart with a full soup in your inventory.
It is the riskiest kit on the list, and one of the fastest to end a duel.