In the past month or two, Tripwire has been playing fast and loose with the size of its dismemberable heads and torsos over the course of its Weekly Outbreak events. This week's new mutator, Beefcake, embiggens zeds that score hits against you.
Tripwire tells me via email:
"Whenever Zeds damage a player they get bigger and gain more health. they also become more dangerous because their reach also increases. Be sure to kill Sirens and King Crawlers quickly because the siren scream will 'grow' any Zeds in her scream radius. The king crawler and Zeds that pass through the gas cloud will also 'grow.'"
Beat the event on Suicidal difficulty and you'll earn the Horzine Armor Precious, a golden suit that'll match the helmet featured in a different Outbreak last month. This is one of the last KF2 Weekly Outbreaks, which Tripwire creative director Bill Munk last month at E3. Here's next week's event, the final one of the summer:
August 8—Boom - Zeds under pressure; may explode.
Maybe it was something they ate? Bad gas? Whatever it was, Zeds explode when killed in this outbreak.