After rocketing higher yesterday (apparently thanks to the $9B valuation given to Twitter by BlackRock), Zynga (ZNGA -7.6%) is giving back a big chunk of those gains today. Groupon (GRPN -2.3%) is also retracing its steps a bit. Zynga still has a sizable short interest, but it's well below last summer's peak. The company's Q4 report is due on Feb. 5, and Groupon's on Feb. 27. Facebook reports tomorrow.