This trap comes from the book Invisible Chess Moves: Discover Your Blind Spots and Stop Overlooking Simple Wins by Emmanuel Neiman and Yochanan Afek. In the Chameleon Sicilian, 1.e4 c5 2.Ne2 (other move orders are also possible), White often keeps Black guessing for several moves as to whether he will play an Open Sicilian with d4, or a Closed Sicilian with g3, Bg2, etc. In the latter case, if White holds off on Nbc3 he can try to take over the center with c3 and d4.
The Chameleon can be tricky for Black if his preferred system against the Closed doesn't mesh well with his preferred Open Sicilian. In Bacrot-Relange, Black responded with 2...d6 (a Najdorf player would be unhappy after 2...Nc6 3.d4) 3.g3 d5!? Now 3.cxd5 Qxd5 would be awkward for White. Best may be the gambit 3.Bg2 dxe4 4.Nbc3!?, when 4...f5!? 5.0-0 Nf6 6.d3 exd3 7.Nf4 Nc6 8.Re1 dxc2 9.Bxc6+ bxc6 10.Qxc2 gave White compensation for the two sacrificed pawns in Baklan (2618)-Tukhaev (2466), Alushta 2007 (1/2-1/2, 38). Bacrot preferred 4.Nbc3, and after 4...d4! he should have retreated with 5.Nb1. Instead, he lunged forward with the aggressive-looking 5.Nd5??, overlooking Relange's surprising 5...g5! trapping the knight. After 6.d3 h6! (avoiding 6...e6? 7.Bxg5!) 7.Bg2 e6, White was losing a piece for just one pawn. Although he fought on, the outcome was never in doubt.