Obvious stand-in for the close-up of Rolf de Maré getting kicked in head, which sends him (via reverse motion) flying back into the end title. The "kick" itself is clearly achieved through reverse motion.
The conclusion was supposed to surprise the viewer by having Rolf de Maré suddenly burst through the end title "FIN". But first he pokes a hole through the title screen from behind - presumably to see where he is jumping - and this spoils the gag somewhat.