This is a very archaic word that’s now found only in old Tagalog literary texts.
nagsisisila
(that are) killing
nagsisisila
slaughtering
(by wild animals)
If there is one animal doing the killing (by eating), the verb form is nagsisila. If there are many animals engaged in the killing, the verb form is nagsisisila.
The following line is from Florante at Laura by Balagtas.
hyena’t tigreng ganid na nagsisisila
When a tiger “eats” another animal, it is in effect slaughtering the animal.
KAHULUGAN SA TAGALOG
nagsisila: pumapatay (pagkain ng hayop)
salitang ugat: silà
silà:pagsakmal sa pagkain ng malakíng hayop upang kumain
siláin, sumilà, sinisila
misspelling: nagisila