Zwischenzug is German for "in-between move," and it names one of the sneakiest habits in chess: when your opponent expects an automatic reply, usually a recapture, you insert something stronger first. Their move assumed a script; you tear it up.
The habit to build: recaptures are the most automatic moves in chess, and automatic is exactly where blunders hide, in both directions. Before you recapture, take three seconds to ask: do I have a check, a mate, or a bigger threat instead? And before you capture something, ask what in-between moves YOUR opponent gets before recapturing.
8
7
6
5
4
3
2
a1
b
c
d
e
f
g
h
Black just grabbed a knight on g5 and attacks the bishop on d2, expecting Bxg5 in reply.
Black expects the recapture on g5. Play something stronger.
8
7
6
5
4
3
2
a1
b
c
d
e
f
g
h