  Using 2D numerical hydrodynamical simulations of type Ia supernova remnants
(SNR Ia) we show that iron clumps few times denser than the rest of the SN
ejecta might form protrusions in an otherwise spherical SNR. Such protrusions
exist in some SNR Ia, e.g., SNR 1885 and Tycho. Iron clumps are expected to
form in the deflagration to detonation explosion model. In SNR Ia where there
are two opposite protrusions, termed ears, such as Kepler's SNR and SNR
G1.9+0.3, our scenario implies that the dense clumps, or iron bullets, were
formed along an axis. Such a preferred axis can result from a rotating white
dwarf progenitor. If our claim holds, this offers an important clue to the SN
Ia explosion scenario.
