Remove ‘a’ in part 2. Article is not used before phrases such as in danger, in fact, in debt, in confusion, in demand, in detail etc.
The correct sentence should be: It was by mistake that he caught his hand.
|By post, by chance, by messenger, by cheque, by air, by land, by sea, by road, by car, by bus, by jeep, by train, by plane, by steamer, by scooter, by bicycle, by mistake|
|In fact, in detail, in short, in trouble, in confusion, in time, in demand, in danger, in life, in haste, in crisis, in difficulty, in doubt, in debt.|
|Write in ink, write in pencil|