  The repeating FRB 121102 emitted a pair of discrete bursts separated by 37 ms
and another pair, 131 days later, separated by 34 ms, during observations that
detected FRB at a mean rate of $2 \times 10^{-4}$/s. Here I assume that these
events are separate bursts rather than multiple peaks from longer single bursts
and consider their implications. They then are inconsistent with Poissonian
statistics. The measured intervals constrain any possible periodic modulation
underlying the highly episodic emission. If more such short intervals are
measured a period may be determined or periodicity may be excluded. Sources of
narrow wandering beams predict pairs (or higher multiples) of bursts closely
spaced in time compared to the mean event rate.
