Detailed scan at week 21

Went for the routine detailed scan, the procedure went well and it was confirmed with picture that it is one boy and one girl. The scan started well with the focus on baby 1, which is ah girl. Girl is hyperactive and refuse to stay at one positon long enough for the detailed to be capture, so it took us awhile to see everything. When come to the Boy, it is the direct opposite. Ah boy refuse to move and stayed on the same postion that his face feature detailed can't be seen. When the Doc try to move him, he covered his face with his hands...why are they so different. I went for a walk, came back for the scan and he is still in the same position. Ended up, I have to go back to KKH for the scan again on Monday. Ah boy, now the scan is double the cost...happy???