  We present study of a typical explosive event (EE) at sub-arcsecond scale
witnessed by strong non-Gaussian profiles with blue- and red-shifted emission
of up to 150 km/s seen in the transition-region Si IV 1402.8 \AA, and the
chromospheric Mg II k 2796.4 \AA\ and C II 1334.5 \AA\ observed by the
Interface Region Imaging Spectrograph at unprecedented spatial and spectral
resolution. For the first time a EE is found to be associated with very
small-scale ($\sim$120 km wide) plasma ejection followed by retraction in the
chromosphere. These small-scale jets originate from a compact bright-point-like
structure of $\sim$1.5" size as seen in the IRIS 1330 \AA\ images. SDO/AIA and
SDO/HMI co-observations show that the EE lies in the footpoint of a complex
loop-like brightening system. The EE is detected in the higher temperature
channels of AIA 171 \AA, 193 \AA\ and 131 \AA\ suggesting that it reaches a
higher temperature of log T$=5.36\pm0.06$ (K). Brightenings observed in the AIA
channels with durations 90--120 seconds are probably caused by the plasma
ejections seen in the chromosphere. The wings of the C II line behave in a
similar manner as the Si IV's indicating close formation temperatures, while
the Mg II k wings show additional Doppler-shifted emission. Magnetic
convergence or emergence followed by cancellation at a rate of $5\times10^{14}$
Mx s$^{-1}$ is associated with the EE region. The combined changes of the
locations and the flux of different magnetic patches suggest that magnetic
reconnection must have taken place. Our results challenge several theories put
forward in the past to explain non-Gaussian line profiles, i.e. EEs. Our case
study on its own, however, cannot reject these theories, thus further in-depth
studies on the phenomena producing EEs are required.
