  We analyzed spectral and imaging data from the Interface Region Imaging
Spectrograph (IRIS), images from the Atmospheric Imaging Assembly (AIA) aboard
the Solar Dynamics Observatory (SDO), and magnetograms from the Helioseismic
and Magnetic Imager (HMI) aboard SDO. We report observations of small flaring
loops in the penumbra of a large sunspot on July 19, 2013. Our main event
consisted of a loop spanning ~ 15 arcsec, from the umbral-penumbral boundary to
an opposite polarity region outside the penumbra. It lasted approximately 10
minutes with a two minute impulsive peak and was observed in all AIA/SDO
channels, while the IRIS slit was located near its penumbral footpoint. Mass
motions with an apparent velocity of ~ 100 km/s were detected beyond the
brightening, starting in the rise phase of the impulsive peak; these were
apparently associated with a higher-lying loop. We interpret these motions in
terms of two-loop interaction. IRIS spectra in both the C II and Si IV lines
showed very extended wings, up to about 400 km/s, first in the blue (upflows)
and subsequently in the red wing. In addition to the strong lines, emission was
detected in the weak lines of Cl I, O I and C I as well as in the Mg II triplet
lines. Absorption features in the profiles of the C II doublet, the Si IV
doublet and the Mg h and k lines indicate the existence of material with a
lower source function between the brightening and the observer. We attribute
this absorption to the higher loop and this adds further credibility to the
two-loop interaction hypothesis. We conclude that the absorption features in
the C II, Si IV and Mg II profiles originate in a higher-lying, descending
loop; as this approached the already activated lower-lying loop, their
interaction gave rise to the impulsive peak, the very broad line profiles and
the mass motions.
