Heureka - from the -Ofun department
Or - running the ackermann function (and possibly other recursive functions) really fast.
Ack(3, 11) = 16381
The latter is optimized C code. Parrot is recompiling (or will do when that's finished) statically known and simple PIR code to native machine code via it's JIT system.
See also a recent post on perl6-internals.