This is a kind of sacrifice, but a very short-lived one... They are not always easy to anticipate, as shown by the nice problem 1, from a recent Chinese beginners' collection (yes, their beginners are not made of the same stuff as ours...)
(;SZ[9]AW[de]AW[ee]AW[cf]AW[ef]AW[cg]AW[eg]AW[bh]AW[fh]AW[ai]AW[bi]AW[fi]AB[cd]AB[dd]AB[ed]AB[be]AB[fe]AB[bf]AB[ff]AB[ag]AB[fg]AB[hg]AB[ah]AB[gh]AB[gi]GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]RU[Japanese]KM[0.00]PB[Noir]
(;B[bg]C[This pretty slow key...]
(;W[dh]C[This pretty slow key...];B[di]C[create this double threat]
(;W[ch]C[create this double threat];B[eh];W[ei];B[eh]C[SnapbackRIGHT])
(;W[eh]C[create this double threat];B[ch];W[ci];B[ch]C[or another oneRIGHT]))
(;W[di];B[dh];W[ch];B[eh]C[RIGHT])
(;W[ch]
(;B[eh]
(;W[dh]
(;B[ei];W[di])
(;B[di];W[ei];B[eh]C[SnapbackRIGHT]))
(;W[di];B[dh]C[RIGHT]))
(;B[dh];W[eh])))
(;B[dh];W[eh]
(;B[dg];W[di];B[ch];W[bg]C[nothing ellse works])
(;B[bg];W[ch])
(;B[ch];W[bg];B[dg];W[di])
(;B[ce];W[di])
(;B[di];W[dg];B[bg];W[ch])
(;B[ci];W[dg];B[bg];W[ch]))
(;B[eh];W[dh];B[di];W[ci]C[here, it is too late])
(;B[di];W[eh]C[there, it isplayed too early])
(;B[ei];W[eh]
(;B[dh];W[ch];B[dg];W[di])
(;B[di];W[ch];B[dh];W[dg])
(;B[ci];W[dh]
(;B[bg];W[ch])
(;B[ch];W[bg])))
(;B[ci];W[ch]
(;B[dh];W[eh];B[dg];W[di])
(;B[eh];W[di];B[ei];W[dh])
(;B[ei];W[eh]))
(;B[ch];W[dh]
(;B[di];W[ci])
(;B[bg];W[ci]))
(;B[dg];W[dh]))