Man-Eating Sliver

All sliver creatures you control have
double strike, as long as a player has at least
one human creature on the battlefield.
Whenever Man-Eating Sliver attacks, Trawl 2
for Humans (Look at the top 2 cards of your
library, you may put any number of human type
creature cards from among them on the battlefield
paying {1} for each of those permanents. Put the
rest back on top of your library in a random order.)