  IceCube is an all-flavor, cubic kilometer neutrino telescope currently under
construction in the deep glacial ice at the South Pole. Its embedded optical
sensors detect Cherenkov light from charged particles produced in neutrino
interactions in the ice. For several years IceCube has been detecting muon
tracks from charged-current muon neutrino interactions. However, IceCube has
yet to observe the electromagnetic or hadronic particle showers or "cascades"
initiated by charged-current or neutral-current neutrino interactions. The
first detection of such an event signature is expected to come from the known
flux of atmospheric electron and muon neutrinos.
  A search for atmospheric neutrino-induced cascades was performed using 275.46
days of data from IceCube's 22-string configuration. Reconstruction and
background rejection techniques were developed to reach, for the first time, a
signal-to-background ratio ~1. Above a reconstructed energy of 5 TeV, 12
candidate events were observed in the full dataset. The signal expectation from
the canonical Bartol atmospheric neutrino flux model is 5.63+-2.25 events,
while the expectation from the atmospheric neutrino flux as measured by
IceCube's predecessor array AMANDA is 7.48 +- 1.50 events. Quoted errors
include the uncertainty on the flux only.
  While a conclusive detection can not yet be claimed because of a lack of
background Monte Carlo statistics, the evidence that we are at the level of
background suppression needed to see atmospheric neutrino-induced cascades is
strong. In addition, one extremely interesting candidate event of energy 133
TeV survives all cuts and shows an intriguing double pulse structure in its
waveforms that may signal the "double bang" of a tau neutrino interaction.

High Energy Astrophysical Phenomena