Possible Clues:

• Delighted being second, then went in front
• Mo was in first place – that's caused amusement
• ___ pink
• Delighted to have credit spent?
• Blood-sucking mite was first to get excited
• Amused mark of approval came first
• Happy parasite was ahead of salmon
• Amused; second was in first place
• Amused moment was among the first
• Made to giggle